Nanocrystals including a group IIIA element and a group VA element, method, composition, device and other products

ABSTRACT

A nanocrystal comprising a semiconductor material comprising one or more elements of Group IIIA of the Periodic Table of Elements and one or more elements of Group VA of the Periodic Table of Elements, wherein the nanocrystal is capable of emitting light having a photoluminescence quantum efficiency of at least about 30% upon excitation. Also disclosed is a nanocrystal including a core comprising a first semiconductor material comprising one or more elements of Group IIIA of the Periodic Table of Elements and one or more elements of Group VA of the Periodic Table of Elements, and a shell disposed over at least a portion of the core, the shell comprising a second semiconductor material, wherein the nanocrystal is capable of emitting light having a photoluminescence quantum efficiency of at least about 30% upon excitation. Also disclosed is a nanocrystal comprising a nanocrystal core and a shell comprising a semiconductor material disposed on at least a portion of the nanocrystal core, wherein the semiconductor material comprises at least three chemical elements and is obtainable by a process comprising adding a precursor for at least one of the chemical elements of the semiconductor material from a separate source to a nanocrystal core while simultaneously adding amounts of precursors for the other chemical elements of the semiconductor material. A population of nanocrystals, method for preparing nanocrystals, compositions, and devices including nanocrystals are also disclosed.

This application is a continuation of U.S. patent application Ser. No.13/740,379 filed 14 Jan. 2013, which is a continuation of U.S. patentapplication Ser. No. 12/454,706, filed 21 May 2009, which is acontinuation of commonly owned PCT Application No. PCT/US2007/024320filed 21 Nov. 2007, which was published in the English language as PCTPublication No. WO 2008/133660 on 6 Nov. 2008. The PCT Applicationclaims priority to U.S. Application No. 60/866,822 filed 21 Nov. 2006.The disclosures of each of the foregoing applications are herebyincorporated herein by reference in their entireties.

TECHNICAL FIELD OF THE INVENTION

The technical field of the present invention relates to nanocrystals,methods for preparing nanocrystals, and devices including nanocrystals.

SUMMARY OF THE INVENTION

In accordance with one aspect of the present invention, there isprovided a nanocrystal comprising a semiconductor material comprisingone or more elements of Group IIIA of the Periodic Table of Elements andone or more elements of Group VA of the Periodic Table of Elements,wherein the nanocrystal is capable of emitting light having aphotoluminescence quantum efficiency of at least about 30% uponexcitation.

In certain embodiments, the size of a nanocrystal can be, for example,from about 1 to about 20 nm. In certain embodiments, the size of ananocrystal can be from about 1 to about 6 nm, from about 1 to about 5nm, from about 1 to about 4 nm, from about 1 to about 3 nm, from about 1to about 2 nm.

Advantageously, in certain embodiments efficient photoluminescenceperformance can be achieved without requiring nanocrystal etching, e.g.,with a fluorine containing composition, e.g., HF.

In certain embodiments, the nanocrystal is capable of emitting lightincluding a maximum peak emission at a wavelength in the range fromabout 500 nm to about 700 nm upon excitation. In certain embodiments,the maximum peak emission has a full width at half maximum (FWHM) ofless than or equal to 70 nm, less than or equal to 60 nm, less than orequal to 50 nm, less than or equal to 40 nm, or less than or equal to 30nm.

In certain embodiments, the nanocrystal is capable of emitting lightincluding a maximum peak emission at a wavelength in the range fromabout 560 nm to about 650 nm upon excitation.

In certain embodiments, the nanocrystal can further include one or moreligands attached to the surface of the nanocrystal.

In accordance with another aspect of the present invention, there isprovided a nanocrystal including a core comprising a first semiconductormaterial comprising one or more elements of Group IIIA of the PeriodicTable of Elements and one or more elements of Group VA of the PeriodicTable of Elements, and a shell disposed over at least a portion of thecore, the shell comprising a second semiconductor material, wherein thenanocrystal is capable of emitting light having a photoluminescencequantum efficiency of at least about 30% upon excitation.

In certain embodiments, the nanocrystal is capable of emitting lightincluding a maximum peak emission at a wavelength in the range fromabout 500 nm to about 700 nm upon excitation. In certain embodiments,the maximum peak emission has a full width at half maximum (FWHM) of notmore than 70 nm, not more than 60 nm, not more than 50 nm, not more than40 nm, or not more than 30.

In certain embodiments, the nanocrystal is capable of emitting lightincluding a maximum peak emission at a wavelength in the range fromabout 570 nm to about 650 nm upon excitation.

In certain embodiments, a core/shell nanocrystal can have an averagediameter from, for example, about 3 to about 55 nm, from about 3 toabout 40 nm, from about 3 to about 25 nm, from about 3 to about 10 nm.In certain embodiments, the average diameter of a nanocrystal core canbe, for example, from about 1 to about 7 nm, from about 1 to about 4 nm,from about 2 to about 3 nm, from about 4 to about 7 nm. An example of anaverage thickness for a shell is from about 1 to about 3 nm, whichcorresponds to an approximately 10 monolayer thickness. (In suchexample, a monolayer thickness would be approximately from about 1 toabout 3 Angstroms.) The actual monolayer thickness is dependent upon thesize and composition of the molecules included in the shell.

In certain embodiments, the shell is disposed over, for example, atleast 60%, at least 70%, at least 80%, at least 90% of a surface of thenanocrystal core. In certain preferred embodiment, the nanocrystal coreis substantially completely (e.g., greater than 95%, greater than 96%,greater than 97%, greater than 98%, greater than 99%) overcoated withthe shell.

In certain embodiments, the nanocrystal can include one or more ligandsattached to the surface of the nanocrystal.

In certain embodiments, the nanocrystal core on which the shell isdisposed is capable of emitting light having a photoluminescence quantumefficiency of at least about 3% upon excitation prior to disposition ofa shell thereon.

In accordance with another aspect of the invention, there is provided apopulation of nanocrystals comprising a semiconductor materialcomprising one or more elements of Group IIIA of the Periodic Table ofElements and one or more elements of Group VA of the Periodic Table ofElements, wherein the population is capable of emitting light having aphotoluminescence quantum efficiency of at least about 30% uponexcitation, and wherein the light emitted by the population has a FWHMno greater than about 70 nm.

In accordance with another aspect of the present invention, there isprovided a population of nanocrystals, wherein the nanocrystals comprisea core comprising a first semiconductor material comprising one or moreelements of Group IIIA of the Periodic Table of Elements and one or moreelements of Group VA of the Periodic Table of Elements, and a shelldisposed over at least a portion of the core, the shell comprising asecond semiconductor material, wherein the population is capable ofemitting light having a photoluminescence quantum efficiency of at leastabout 30% upon excitation.

In accordance with another aspect of the present invention, there isprovided a nanocrystal core comprising a semiconductor materialcomprising one or more elements of Group IIIA of the Periodic Table ofElements and one or more elements of Group VA of the Periodic Table ofElements, wherein the nanocrystal core is capable of emitting lighthaving a photoluminescence quantum efficiency of at least about 3% uponexcitation In certain embodiments, the average diameter of thenanocrystal core can be, for example, from about 1 to about 7 nm, fromabout 1 to about 4 nm, from about 2 to about 3 nm, from about 4 to about7 nm.

In accordance with one aspect of the invention, there is provided amethod for preparing a nanocrystal comprising a semiconductor materialcomprising one or more elements of Group IIIA of the Periodic Table ofElements and one or more elements of Group VA of the Periodic Table ofElements, the method comprising dispersing one or more Group IIIAprecursors in a first solvent to form one or more Group IIIA reactants;dispersing one or more Group VA precursors in a second solvent to formone or more Group VA reactants; mixing the one or more Group IIIAreactants and the one or more Group VA reactants to form a reactionmixture, and adding an acid to the reaction mixture to promote reactionof the reactants to form nanocrystals of the semiconductor material.Optionally, an amine is also present in the reaction mixture prior tothe addition of the acid.

Preferably the acid comprises a carboxylic acid. Examples of certainpreferred embodiments include, but are not limited to,CH₃(CH₂)_(n)C(O)OH wherein n=6-18 (e.g., octanoic [caprylic] acid,nonanoic [pelargonic] acid, decanoic [capric] acid, undecanoic acid,dodecanoic [lauric] acid, tridecanoic acid, tetradecanoic [myristic]acid, pentadecanoic acid, hexadecanoic [palmitic] acid, heptadecanoic[margaric] acid, octadecanoic [stearic] acid, nonadecanoic acid,eicosanoic [arachidic] acid), and mixtures of any two or more of theforegoing). Other non-limiting examples include 9-octadecenoic [oleic]acid. Other suitable acids can be readily ascertained by one of ordinaryskill in the art. In certain embodiments, the acid can also act as aligand source.

In certain more preferred embodiments, the acid is dispersed in a thirdsolvent before being added to the reaction mixture.

Solvents, Group IIIA and Group VA precursors, and optional amines arediscussed in more detail below.

In accordance with a further aspect of the present invention, there isprovided a method for preparing a nanocrystal comprising a semiconductormaterial comprising one or more elements of Group IIIA of the PeriodicTable of Elements and one or more elements of Group VA of the PeriodicTable of Elements. The method comprises dispersing one or more GroupIIIA precursors in a first solvent to form one or more Group IIIAreactants; dispersing one or more Group VA precursors in a secondsolvent to form one or more Group VA reactants; and reacting the one ormore Group IIIA reactants with one or more Group VA reactants in thepresence of a ligand source in a third solvent to form nanocrystalshaving one or more ligands attached to at least a portion of thenanocrystals.

In certain preferred embodiments of the methods of the presentinvention, the first solvent comprises a coordinating solvent, thesecond solvent comprises a non-coordinating solvent, and the thirdsolvent comprises a non-coordinating solvent. In certain embodiments,the second and third solvents are preferably the same. Preferably, eachof the solvents is a liquid at room temperature for convenience.

In certain embodiments, the first solvent can comprise anon-coordinating solvent. In certain embodiments, the first solvent cancomprise a mixture of solvents. In certain preferred embodiments, thefirst solvent comprises a coordinating solvent. In certain preferredembodiments, the first solvent comprises methyl myristate, dioctyl etheror other high boiling point ether, diphenyl oxide, biphenyl, a mixture,more preferably a eutectic mixture, comprising biphenyl and diphenyloxide, including, e.g., DOWTHERM A, available from the Dow ChemicalCompany.

In certain preferred embodiments of the methods of the presentinvention, the second solvent comprises a non-coordinating solvent. Incertain embodiments, the second solvent comprises a mixture of solvents.

In certain preferred embodiments of the methods of the presentinvention, the third solvent comprises a non-coordinating solvent. Incertain embodiments, the third solvent comprises a mixture of solvents.

In certain embodiments of the methods of the present invention, at leasta portion of the one or more Group IIIA precursors dissolve in the firstsolvent to form one or more Group IIIA reactants and the at least aportion of the one or more Group VA precursors dissolve in the secondsolvent to form one or more Group VA reactants

In certain embodiments, one or more Group IIIA reactants can be reactedwith one or more Group VA reactants in the presence of a ligand sourceand an amine.

In certain embodiments, the method comprises dispersing one or moreGroup IIIA precursors in a first solvent to form one or more Group IIIAreactants; dispersing one or more Group VA precursors in a secondsolvent to form one or more Group VA reactants; adding one or more GroupIIIA reactants and one or more Group VA reactants to a reaction mediumincluding a third solvent and a ligand source to form a reactionmixture, and reacting the reaction mixture under conditions sufficientto form nanocrystals of the semiconductor material having apredetermined composition, predetermined size, and predeterminedemission characteristics, at least a portion of the nanocrystalsincluding one or more ligands attached thereto.

A description of first, second, and third solvents is provided above.

In certain embodiments, the reaction medium further includes an amine.

Examples of Group IIIA precursors include elements, covalent compounds,or ionic compounds, including coordination complexes or a metal salt,that serve as a source for the electropositive element or elements inthe resulting nanocrystal. Examples of Group VA precursors includeelements, covalent compounds, or ionic compounds that serve as a sourcefor the electronegative element or elements in the resultingnanocrystal. In certain embodiments, binary materials, ternarymaterials, quaternary materials, and even more complex species may beprepared using the method, in which case more than one Group IIIAprecursor and/or more than one Group VA precursor are included.

For example, a Group IIIA precursor can constitute a wide range ofsubstances, such as a metal oxide, a metal carbonate, a metalbicarbonate, a metal sulfate, a metal sulfite, a metal phosphate, metalphosphite, a metal halide, a metal carboxylate, a metal alkoxide, ametal thiolate, a metal amide, a metal imide, a metal alkyl, a metalaryl, a metal coordination complex, a metal solvate, a metal salt, andthe like. Non-limiting examples of indium precursors include InMe₃,In(III) acetate, In(III) trifluoroacetate, InR₃ (wherein R=ethyl,propyl, butyl, pentyl, hexyl, isopropyl, isobutyl, tert-butyl). Othersuitable Group IIIA precursors can be readily ascertained by one ofordinary skill in the art.

Group VA precursors are most often selected from the element itself(oxidation state 0), covalent compounds, or ionic compounds of the groupV elements (N, P, As, or Sb). Non-limiting examples of phosphorusprecursors include P(SiR₃)₃ wherein R=methyl, ethyl, propyl, butyl,pentyl, hexyl, isopropyl, isobutyl, tert-butyl). Other suitable Group VAprecursors can be readily ascertained by one of ordinary skill in theart.

In a typical preparation, the ligand is selected from fatty acids,amines, phosphines, phosphine oxides, or phosphonic acids.

Examples of a preferred ligand source include carboxylic acids. Incertain preferred embodiments, the ligand source comprisesCH₃(CH₂)_(n)C(O)OH wherein n=6-18 (e.g., octanoic [caprylic] acid,nonanoic [pelargonic] acid, decanoic [capric] acid, undecanoic acid,dodecanoic [lauric] acid, tridecanoic acid, tetradecanoic [myristic]acid, pentadecanoic acid, hexadecanoic [palmitic] acid, heptadecanoic[margaric] acid, octadecanoic [stearic] acid, nonadecanoic acid,eicosanoic [arachidic] acid), and mixtures of any two or more of theforegoing). Other non-limiting examples include 9-octadecenoic [oleic]acid. Other suitable ligand sources can be readily ascertained by one ofordinary skill in the art.

Examples of amines include, but are not limited to, secondary amines,e.g., (CH₃(CH₂)_(n))₂NH wherein n=3-11 (e.g., dibutylamine,dipentylamine, dihexylamine, diheptylamine, dioctylamine, dinonylamine,didecylamine, didundecylamine, didodecylamine), etc.; and primaryamines, e.g., CH₃(CH₂)_(n)NH₂ wherein n=5-19 (e.g., hexylamine,heptylamine, octylamine, nonylamine, decylamine, undecylamine,dodecylamine, tridecylamine, tetradecylamine, pentadecylamine,hexadecylamine, heptadecylamine, octadecylamine, nonadecylamine,eicosylamine). Other suitable amines can be readily ascertained by oneof ordinary skill in the art.

Examples of suitable coordinating solvents include, but are not limitedto, octadecene, squalene, methyl myristate, octyl octanoate, hexyloctanoate, and CH₃(CH₂)_(n)C(O)O(CH₂)_(m)CH₃ wherein n=4-18 and m=1-8,dioctyl ether, and diphenyl ether, and mixtures of one or more solvents.A preferred mixture comprises a mixture, more preferably a eutecticmixture, of biphenyl and diphenyl oxide, including, e.g., DOWTHERM A,available from the Dow Chemical Company. Other high boiling point ethers(e.g., BP>˜200° C.) may also be used. Such ethers (coordinating) can bearomatic ethers, aliphatic ethers or aromatic aliphatic ethers. Examplesof additional ethers include, but are not limited to, dihexyl ether,diethyleneglycol dimethyl ether, diethyleneglycol dibutyl ether,triethyleneglycol dimethyl ether, tetraethyleneglycol dimethyl ether,butyl phenyl ether, benzyl phenyl ether, dibenzyl ether, ditolyl etherand isomers thereof. Mixtures of two or more solvents can also be used.Other suitable coordinating solvents can be readily ascertained by oneof ordinary skill in the art.

Most preferably the coordinating first and/or second solvent included inthe methods of the invention does not include alkyl phosphines, alkylphosphine oxides, alkyl phosphonic acids, alkyl phosphinic acids,pyridine, tri-n-octyl phosphine (TOP), tri-n-octyl phosphine oxide(TOPO), trishydroxylpropylphosphine (tHPP), or other coordinatingsolvents that include a phosphorus or nitrogen atom.

Examples of suitable non-coordinating solvents include, but are notlimited to, squalane, octadecane, or any other saturated hydrocarbonmolecule. Mixtures of two or more solvents can also be used. Othersuitable non-coordinating solvents can be readily ascertained by one ofordinary skill in the art. In certain embodiments, non-coordinatingsolvents comprise liquids having a dipole moment in the range form 0 toabout 0.2 μ/D. In certain embodiments, coordinating solvents compriseliquids having a dipole moment from 0.7 to 4 μ/D (e.g., stronglycoordinating) or liquids having a dipole moment in the range from 0.2 to0.7 μ/D (e.g., weakly coordinating).

In certain embodiments, the reaction is carried out in an inertatmosphere. In certain embodiments, the reaction is carried out in acontrolled atmosphere (substantially free of moisture and air).

In certain embodiments, the nanocrystal prepared is capable of emittinglight having a photoluminescence quantum efficiency of at least about30% upon excitation.

In certain embodiments, the method further includes forming a shellcomprising one or more additional semiconductor materials over at leasta portion of the surface of at least a portion of the nanocrystal. Incertain preferred embodiments, the one or more additional semiconductormaterials are different from the semiconductor material included in thenanocrystal.

In certain embodiments, the nanocrystal is isolated from the reactionmixture and purified before the shell is formed.

In certain embodiments, a nanocrystal including a shell further includesone or more ligands attached to the surface of the nanocrystal.

Shell thickness can be varied by growing a desired thickness of theshell. For example, the shell can have a thickness less than about onemonolayer, about one monolayer, or more than about one monolayer.Preferably, the thickness is less than that at which quantum confinementis not achieved. The thickness is selected to achieve the predeterminedcharacteristics of the core/shell nanocrystal. In certain embodiments,the thickness is in the range from greater than about 0 to about 20monolayers. In certain embodiments, the thickness is in the range fromgreater than about 0 to about 10 monolayers. In certain embodiments, thethickness is in the range from greater than about 0 to about 5monolayers. In certain embodiments, the thickness is in the range fromabout 1 to about 5 monolayers. In certain embodiments, the thickness isin the range from about 3 to about 5 monolayers. In certain embodiments,more than 20 monolayers can be grown.

In a further aspect of the present invention there is provided acomposition including a nanocrystal comprising a semiconductor materialcomprising one or more elements of Group IIIA of the Periodic Table ofElements and one or more elements of Group VA of the Periodic Table ofElements, wherein the nanocrystal is capable of emitting light having aphotoluminescence quantum efficiency of at least about 30% uponexcitation.

In certain embodiments, the nanocrystal includes a core comprising afirst semiconductor material comprising one or more elements of GroupIIIA of the Periodic Table of Elements and one or more elements of GroupVA of the Periodic Table of Elements, and a shell disposed over at leasta portion of the core, the shell comprising a second semiconductormaterial, wherein the nanocrystal is capable of emitting light having aphotoluminescence quantum efficiency of at least about 30% uponexcitation. Examples of first semiconductor materials and secondsemiconductor materials are described above and in the detaileddescription.

In certain embodiments, the luminescence includes a maximum peakemission with a full width at half maximum (FWHM) of not more than 70nm, not more than 60 nm, not more than 50 nm, not more than 40 nm, ornot more than 30.

In certain embodiments, the nanocrystal is capable of emitting lightincluding a maximum peak emission at a wavelength in the range fromabout 500 nm to about 700 nm upon excitation. In certain embodiments,the maximum peak emission has a full width at half maximum (FWHM) of notmore than 70 nm, not more than 60 nm, not more than 50 nm, not more than40 nm, or not more than 30.

In certain embodiments, the nanocrystal is capable of emitting lightincluding a maximum peak emission at a wavelength in the range fromabout 560 nm to about 650 nm upon excitation.

In certain embodiment, the composition further includes a polymer. Incertain embodiments, the composition further includes a pre-polymer.

In certain embodiments, the composition further includes an oligomer.

In certain embodiments, the composition further includes a smallmolecule.

In certain embodiments, the composition further includes an inorganicmaterial.

In certain embodiments, the composition comprises a matrix. The matrixcan comprise an organic or inorganic material.

In certain embodiments, the semiconductor nanocrystals are dispersed inthe matrix. In certain embodiments, the semiconductor nanocrystals arerandomly dispersed in the matrix. In certain embodiments, thesemiconductor nanocrystals are homogeneously dispersed in the matrix.

Non-limiting examples of matrices include, but are not limited to, apolymer (e.g., polystyrene, epoxy, polyimides), a glass (e.g., silicaglass), a gel (e.g., a silica gel), and any other material which is atleast partially, and preferably fully, transparent to the light emittedby the semiconductor nanocrystals and in which semiconductornanocrystals can be included. Depending on the use of the composition,the matrix can be conductive or non-conductive. Examples of preferredmatrices include, but are not limited to, glass or a resin. Resins canbe non-curable resins, heat-curable resins, or photocurable resins. Morespecific examples of resins can be in the form of either an oligomer ora polymer, a melamine resin, a phenol resin, an alkyl resin, an epoxyresin, a polyurethane resin, a maleic resin, a polyamide resin,polymethyl methacrylate, polyacrylate, polycarbonate, polyvinyl alcohol,polyvinylpyrrolidone, hydroxyethylcellulose, carboxymethylcellulose,copolymers containing monomers forming these resins, and the like.Examples of a photo-polymerizable resin include an acrylic acid ormethacrylic acid based resin containing a reactive vinyl group, aphoto-crosslinkable resin which generally contains a photo-sensitizer,such as polyvinyl cinnamate, or the like. A heat-curable resin mayselected when the photo-sensitizer is not used. Matrix resins may beused individually or in combination of two or more. Other matrixmaterials can be readily identified by one of ordinary skill in the art.In certain embodiments, a composition including a matrix may furtherinclude scatterers (e.g., without limitation, metal or metal oxideparticles, air bubbles, and glass and polymeric beads (solid or hollow),and/or other optional additives typically used in the desired end-useapplication for the composition.

In certain embodiments, the composition further includes a liquidmedium. In certain embodiments, compositions in accordance with thepresent invention including a liquid medium comprise an ink. Examples ofsuitable liquids and other optional additives that may be included in anink are described in International Application No. PCT/US2007/00873 ofSeth Coe-Sullivan et al., for “Composition Including Material, MethodsOf Depositing Material, Articles Including Same And Systems ForDeposition Material”, filed 9 Apr. 2007, and International ApplicationNo. PCT/US2007/014711 of Seth Coe-Sullivan et al., for “Methods ForDepositing Nanomaterial, Methods For Fabricating A device, And MethodsFor Fabricating An Array Of Devices”, filed 25 Jun. 2007, which are eachhereby incorporated herein by reference in their entireties.

In certain embodiments, the composition further includes a non-polarliquid in which the semiconductor nanocrystal is dispersible.

In certain embodiments, the composition further includes a polar liquidin which the semiconductor nanocrystal is dispersible.

In accordance with a still further aspect of the present invention thereis provided a device including a nanocrystal comprising a semiconductormaterial comprising one or more elements of Group IIIA of the PeriodicTable of Elements and one or more elements of Group VA of the PeriodicTable of Elements, wherein the nanocrystal is capable of emitting lighthaving a photoluminescence quantum efficiency of at least about 30% uponexcitation.

In certain embodiments, a nanocrystal includes a core comprising a firstsemiconductor material comprising one or more elements of Group IIIA ofthe Periodic Table of Elements and one or more elements of Group VA ofthe Periodic Table of Elements, and a shell disposed over at least aportion of the core, the shell comprising a second semiconductormaterial, wherein the nanocrystal is capable of emitting light having aphotoluminescence quantum efficiency of at least about 30% uponexcitation. Examples of first semiconductor materials and secondsemiconductor materials are described above and in the detaileddescription.

In certain embodiments, the luminescence includes a maximum peakemission with a full width at half maximum of not more than 70 nm, notmore than 60 nm, not more than 50 nm, not more than 40 nm, or not morethan 30 nm.

In certain embodiments, the nanocrystal is capable of emitting lightincluding a maximum peak emission at a wavelength in the range fromabout 500 nm to about 700 nm upon excitation. In certain embodiments,the maximum peak emission has a full width at half maximum (FWHM) of notmore than 70 nm, not more than 60 nm, not more than 50 nm, not more than40 nm, or not more than 30.

In certain embodiments, the nanocrystal is capable of emitting lightincluding a maximum peak emission at a wavelength in the range fromabout 560 nm to about 650 nm upon excitation.

In accordance with another aspect of the present invention, there isprovided a device including a nanocrystal comprising a semiconductormaterial comprising one or more elements of Group IIIA of the PeriodicTable of Elements and one or more elements of Group VA of the PeriodicTable of Elements, wherein the device further includes less than 1,000ppm Pb, less than 100 ppm Cd, and less than 1,000 ppm Hg.

In certain embodiments of devices in accordance with various aspects ofthe present invention, the device comprises a light emitting devicewhich includes a first electrode a second electrode opposed to the firstelectrode, and a plurality of nanocrystals in accordance with theinvention disposed between the first electrode and the second electrode.In certain embodiments, one of the electrodes can be supported by asubstrate (which can be flexible or rigid).

In certain embodiments of devices in accordance with various aspects ofthe present invention, a light emitting device includes a firstelectrode a second electrode opposed to the first electrode, and aplurality of nanocrystals comprising a nanocrystal comprising one ormore elements of Group IIIA of the Periodic Table of Elements and one ormore elements of Group VA of the Periodic Table of Elements, and thedevice includes less than 1,000 ppm Pb, less than 100 ppm Cd, and lessthan 1,000 ppm Hg.

In certain embodiments of devices in accordance with various aspects ofthe present invention, the device can be capable of emitting lightincluding a maximum peak emission in the red region of the spectrum uponexcitation.

In certain other embodiments of devices in accordance with variousaspects of the present invention, the device can comprise a display, alaser, a photoelectric device, a solar cell, and the like.

In accordance with yet another aspect of the present invention, there isprovided a biomedical tag including a nanocrystal in accordance with thepresent invention.

In accordance with yet another aspect of the present invention, there isprovided a catalyst including a nanocrystal in accordance with thepresent invention.

In accordance with yet a further aspect of the present invention thereis provided a nanocrystal comprising a nanocrystal core and a shellcomprising a semiconductor material disposed on at least a portion ofthe nanocrystal core, wherein the semiconductor material comprises atleast three chemical elements and is obtainable by a process comprisingadding a precursor for at least one of the chemical elements of thesemiconductor material from a separate source to a nanocrystal corewhile simultaneously adding amounts of precursors for the other chemicalelements of the semiconductor material. The amounts of precursors forthe other chemical elements of the semiconductor material can be addedas a mixture and/or separately (depending on the number of otherprecursors). The amounts of precursor for the other chemical elements ofthe semiconductor material can be also added simultaneously orsequentially.

In certain embodiments, semiconductor material comprises zinc, sulfur,and selenium.

In certain embodiments, the zinc precursor is added separately andselenium and sulfur precursors are added as a mixture.

In certain embodiments, the zinc precursor is added separately andselenium and sulfur precursors are concurrently added from separatesources (e.g., not as a mixture).

In certain preferred embodiments, the molar ratio of the zincprecursor:sulfur precursor:selenium precursor is about 2:1:1. Otherratios can also be used.

In certain embodiments, zinc precursor is added separately and seleniumand sulfur precursors are added sequentially. In certain embodiments,the zinc precursor is added, followed by the selenium precursor,followed by the sulfur precursor.

In certain embodiments, the process is carried out at a temperature andfor a period of time sufficient to form a shell comprising the desiredsemiconductor material at a desired thickness.

In certain embodiments, each of the precursors is added at apredetermined rate. The rate of addition for each precursor can be thesame or different.

Preferably the process is carried out in a liquid medium. In certainembodiments, the liquid medium can comprise a coordinating and/or anon-coordinating solvent. Examples of suitable coordinating andnon-coordinating solvents are described herein. A preferred liquidmedium comprises squalane.

The foregoing, and other aspects described herein all constituteembodiments of the present invention.

It is to be understood that both the foregoing general description andthe following detailed description are exemplary and explanatory onlyand are not restrictive of the invention as claimed. Other embodimentswill be apparent to those skilled in the art from consideration of thedescription, from the claims, and from practice of the inventiondisclosed herein.

DETAILED DESCRIPTION OF THE INVENTION

In accordance with one aspect of the present invention there is provideda nanocrystal comprising a semiconductor material. The semiconductormaterial comprises one or more elements of Group IIIA of the PeriodicTable of Elements and one or more elements of Group VA of the PeriodicTable of Elements, wherein the nanocrystal is capable of emitting lighthaving a photoluminescence quantum efficiency of at least about 30% uponexcitation. A nanocrystal comprising a semiconductor material may alsobe referred to herein as a semiconductor nanoparticle, semiconductornanocrystal, or semiconductor quantum dot.

A semiconductor nanocrystal is capable of emitting light uponexcitation. A semiconductor nanocrystal can be excited by irradiationwith an excitation wavelength of light, by electrical excitation, or byother energy transfer.

Photoluminescence quantum efficiency (also referred to as quantumefficiency, quantum yield or solution quantum yield) represents thepercent of absorbed photons that are reemitted as photons uponexcitation by irradiation with an excitation wavelength of light.

A nanocrystal is a nanometer sized particle, e.g., in the size range ofup to about 1000 nm. In certain embodiments, a nanocrystal can have asize in the range of up to about 100 nm. In certain embodiments, ananocrystal can have a size in the range up to about 20 nm (such asabout 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19,or 20 nm). In certain preferred embodiments, a nanocrystal can have asize less than 100 Å. In certain preferred embodiments, a nanocrystalhas a size in a range from about 1 to about 6 nanometers and moreparticularly from about 1 to about 5 nanometers. The size of ananocrystal can be determined, for example, by direct transmissionelectron microscope measurement. Other known techniques can also be usedto determine nanocrystal size.

Nanocrystals can have various shapes. Examples of the shape of ananocrystal include, but are not limited to, sphere, rod, disk,tetrapod, other shapes, and/or mixtures thereof.

For applications that utilize the luminescent properties of ananocrystal, the nanocrystal size is selected such that the nanocrystalexhibits quantum confinement. Such applications include, but are notlimited to, light-emitting devices, lasers, biomedical tags,photoelectric devices, solar cells, catalysts, and the like.Light-emitting devices including nanocrystals in accordance with thepresent invention may be incorporated into a wide variety of consumerproducts, including, but not limited to, flat panel displays, computermonitors, televisions, billboards, lights for interior or exteriorillumination and/or signaling, heads up displays, fully transparentdisplays, flexible displays, laser printers, telephones, cell phones,personal digital assistants (PDAs), laptop computers, digital cameras,camcorders, viewfinders, micro-displays, vehicles, a large area wall,theater or stadium screen, or a sign. Various control mechanisms may beused to control such devices, including passive matrix and activematrix.

In accordance with another aspect of the present invention, ananocrystal includes a core comprising a first semiconductor materialcomprising one or more elements of Group IIIA of the Periodic Table ofElements (for example, B, Al, Ga, In, and Tl), and one or more elementsof Group VA of the Periodic Table of Elements (for example, nitrogen,phosphorus, arsenic, antimony, and bismuth), and a shell disposed overat least a portion of the core, the shell comprising one or moreadditional semiconductor materials, wherein the nanocrystal is capableof emitting light having a photoluminescence quantum efficiency of atleast about 30% upon excitation. In certain embodiments, a shell cancomprise two or more layers of the same or different semiconductormaterials. In certain embodiments, a layer can include a singlesemiconductor material or a mixture of two or more semiconductormaterials with different compositions, particle sizes, and/or emissioncharacteristics. A semiconductor material may comprise a compound, adoped compound, and/or an alloy. A nanocrystal core surrounded by ashell is also referred to as having a “core/shell” structure.

As discussed above, a semiconductor material that can be included in ashell includes a semiconductor material having a composition that is thesame as or different from the composition of the core. When two or moresemiconductor materials are included in the shell, the shell cancomprise a mixture of the two or more semiconductor materials in asingle layer. In certain embodiments, the two or more semiconductormaterials can be included in the shell as separate layers. In certainother embodiments, the shell can include a layer comprising one or moresemiconductor materials, and one or more additional layers, each ofwhich comprise one or more semiconductor materials. A semiconductormaterial included in the shell can comprise an element, for example, aGroup IVA element. A semiconductor material included in the shell cancomprise a compound represented by the formula MX. In certain examples Mcomprises, for example, one or more elements from Group IA element (forexample, lithium, sodium, rubidium, and cesium), Group IIA (for example,beryllium, magnesium, calcium, strontium, and barium), Group IIB (forexample, Zn, Cd, and Hg), Group IIIA (for example, Al, Ga, In and Tl),Group IVA (for example, Si, Ge, Sn, and Pb), and/or the transitionmetals (for example, Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, W, Mn, Tc, Re, Fe,Co, Ni, Pd, Pt, Rh, and the like). (See, F. A. Cotton et al., AdvancedInorganic Chemistry, 6th Edition, (1999). In certain examples, Xcomprises one or more elements from Group VA (for example, nitrogen,phosphorus, arsenic, antimony, and bismuth) and/or Group VIA (forexample, oxygen, sulfur, selenium, and tellurium). In certainembodiments, a semiconductor material included in the shell comprises abinary (including two elements) material, a ternary (including threeelements) material, a quaternary (including four elements) material,etc. In certain embodiments, the material can comprise an alloy and/or amixture.

Non-limiting examples of a binary semiconductor material that can beincluded in the shell include ZnS, ZnSe, ZnTe, CdS, CdSe, CdTe, HgS,HgSe, HgTe (IIB-VIA materials), PbS, PbSe, PbTe (IVA-VIA materials),AIN, AlP, AlAs, AlSb, GaN, GaP, GaAs, GaSb, InN, InP, InAs, InSb(IIIA-VA materials). Non-limiting examples of ternary semiconductormaterials that can be included in the shell include A_(x)B_(y)C whereinA may comprise a Group IIB, IIIA or IVA element, B may comprise a groupIIB, IIIA, or IVA element, and C may comprise a group VA or VIA element,and x and y are molar fractions between 0 and 1. Preferably x+y=1.

In certain embodiments, the shell can be formed over at least a portionof the core after the core is formed and purified. In certainembodiments, the shell can be formed over at least a portion of the corewith prior purification of the core. In certain embodiments of thelatter case, the formation of the shell can be carried out in the samereaction vessel in which the core is formed.

In certain embodiments, the shell can include semiconductor material(s)having a band gap greater than the band gap of the core material. Incertain other embodiments, the shell can include semiconductormaterial(s) having a band gap less than the band gap of the corematerial.

In certain embodiments, the shell can be chosen so as to have an atomicspacing close to that of the “core” substrate. In certain otherembodiments, the shell and core materials can have the same crystalstructure.

In certain embodiments, the shell is between about 0.1 nm and 10 nmthick. The selection of the semiconductor material included in the shellmay provide for a type I or a type II heterostructure.

Examples of preferred semiconductor materials for inclusion in the shellinclude, without limitation, ZnSe and/or ZnS. A more preferredsemiconductor material for inclusion in the shell includesZnSe_(x)S_(1-x) (wherein 0<x<1); most preferably x is approximately 0.5.

Preparation and manipulation of nanocrystals comprising a semiconductormaterial are described, for example, in U.S. Pat. Nos. 6,322,901 and6,576,291, and U.S. Patent Application No. 60/550,314, each of which ishereby incorporated herein by reference in its entirety. One method ofmanufacturing a nanocrystal, a nanocrystal core, and/or a nanocrystalshell is a colloidal growth process. Colloidal growth occurs byinjection an M donor and an X donor into a hot coordinating ornon-coordinating solvent. One example of a method for preparingmonodisperse nanocrystals comprises pyrolysis of organometallic reagentsinjected into a hot, coordinating solvent. This permits discretenucleation and results in the controlled growth of macroscopicquantities of nanocrystals. The injection produces a nucleus that can begrown in a controlled manner to form a nanocrystal. The reaction mixturecan be gently heated to grow and anneal the nanocrystal. Both theaverage size and the size distribution of the nanocrystals in a sampleare dependent on the growth temperature. The growth temperaturenecessary to maintain steady growth increases with increasing averagecrystal size. The nanocrystal is a member of a population ofnanocrystals. As a result of the discrete nucleation and controlledgrowth, the population of nanocrystals that can be obtained has anarrow, monodisperse distribution of diameters. The monodispersedistribution of diameters can also be referred to as a size. Preferably,a monodisperse population of particles includes a population ofparticles wherein at least about 60% of the particles in the populationfall within a specified particle size range. A population ofmonodisperse particles preferably deviate less than 15% rms(root-mean-square) in diameter and more preferably less than 10% rms andmost preferably less than 5%.

In certain embodiments, the preparation of nanocrystals comprisingsemiconductor material can be carried out in the presence of an amine.See, for example, U.S. Pat. No. 6,576,291 for “Preparation ofNanocrystallites” of Bawendi et al. issued 10 Jun. 2003, which is herebyincorporated herein by reference in its entirety.

A narrow size distribution of the nanocrystals comprising semiconductormaterial allows the possibility of light emission in narrow spectralwidths. Monodisperse semiconductor nanocrystals have been described indetail in Murray et al. (J. Am. Chem. Soc., 115:8706 (1993)); in thethesis of Christopher Murray, “Synthesis and Characterization of II-VIQuantum Dots and Their Assembly into 3-D Quantum Dot Superlattices”,Massachusetts Institute of Technology, September, 1995; and in U.S.patent application Ser. No. 08/969,302 for “Highly LuminescentColor-Selective Materials”. The foregoing documents are herebyincorporated herein by reference in their entireties.

The process of controlled growth and annealing of nanocrystals in asolvent that follows nucleation can also result in uniform surfacederivatization and regular structures. As the size distributionsharpens, the temperature can be raised to maintain steady growth. Byadding more M donor or X donor, the growth period can be shortened. TheM donor can be an inorganic compound, an organometallic compound, orelemental metal. For example, in preparing a semiconductor materialcomprising one or more Group IIIA elements of the Period Table ofElements, M comprises one or more of boron, aluminum, gallium, indium,and thallium. Additional chemical elements can optionally be furtherincluded. In preparing other semiconductor materials, e.g., in preparinga shell, M is selected based on the composition of the desiredsemiconductor material. The X donor is a compound capable of reactingwith the M donor to form a material with the general formula MX. Forexample, in preparing a semiconductor material comprising a Group VAelement of the Period Table of Elements, X comprises one or more ofnitrogen, phosphorus, arsenic, antimony, or bismuth. In preparing othersemiconductor materials, X is selected based on the composition of thedesired semiconductor material. For example, X donor can be achalcogenide (Group VIA) donor or a pnictide (Group VA) donor, such as aphosphine chalcogenide, a bis(silyl)chalcogenide, dioxygen, an ammoniumsalt, or a tris(silyl)pnictide. Examples of suitable X donors include,but are not limited to, dioxygen, bis(trimethylsilyl)selenide((TMS)₂Se), octadecene-Se, trialkyl phosphine selenides such as(tri-n-octylphosphine)selenide (TOPSe) or (tri-n-butylphosphine)selenide(TBPSe), octadecene-Te, trialkyl phosphine tellurides such as(tri-n-octylphosphine)telluride (TOPTe) or hexapropylphosphorustriamidetelluride (HPPTTe), bis(trimethylsilyl)telluride ((TMS)₂Te),octadecene-S, bis(trimethylsilyl)sulfide ((TMS)₂S), a trialkyl phosphinesulfide such as (tri-n-octylphosphine)sulfide (TOPS), an ammonium saltsuch as an ammonium halide (e.g., NH4Cl), tris(trimethylsilyl)phosphide((TMS)₃P), tris(trimethylsilyl)arsenide ((TMS)₃As), ortris(trimethylsilyl)antimonide ((TMS)₃Sb). In certain embodiments, the Mdonor and the X donor can be moieties within the same molecule. Forexample, in preparing ZnSe, M comprises zinc and X comprises selenium.

A solvent can help control the growth of a nanocrystal comprisingsemiconductor material. In preparing a shell, a coordinating solvent canbe used. A coordinating solvent is a compound having at least one donorsite (e.g., a lone electron pair) that, for example, is available tocoordinate to a surface of the growing nanocrystal. Solvent coordinationcan stabilize the growing nanocrystal. Examples of coordinating solventsinclude alkyl phosphines, alkyl phosphine oxides, alkyl phosphonicacids, or alkyl phosphinic acids, however, other coordinating solvents,such as pyridines, furans, and amines may also be suitable for thenanocrystal production. More specific examples of suitable coordinatingsolvents include pyridine, tri-n-octyl phosphine (TOP), tri-n-octylphosphine oxide (TOPO) and trishydroxylpropylphosphine (tHPP). Technicalgrade TOPO can be used. Alternatively, a non-coordinating solvent couldbe used. Examples of non-coordinating solvents include saturatedhydrocarbons; other examples are provided elsewhere herein.

Size distribution during the growth stage of the reaction can beestimated by monitoring the absorption or emission line widths of theparticles. Modification of the reaction temperature in response tochanges in the absorption spectrum of the particles allows themaintenance of a sharp particle size distribution during growth.Reactants can be added to the nucleation solution during crystal growthto grow larger crystals as well as to sharpen size distribution. Forexample, by stopping growth at a particular semiconductor nanocrystalaverage diameter, a population having an average semiconductornanocrystal diameter of less than 150 Å can be obtained. A population ofnanocrystals can have an average diameter of 15 Å to 125 Å. In addition,by stopping growth at a particular semiconductor nanocrystal averagediameter and choosing the proper composition of the semiconductingmaterial, the emission spectra of the semiconductor nanocrystals can betuned continuously over the wavelength range of 300 nm to 5 microns, orfrom 400 nm to 800 nm.

The particle size distribution of the nanocrystals can be furtherrefined by size selective precipitation with a poor solvent for thenanocrystals, such as, for example, methanol/butanol as described inU.S. Pat. No. 6,322,901. For example, nanocrystals can be dispersed in asolution of 10% butanol in hexane. Methanol can be added dropwise tothis stifling solution until opalescence persists. Separation ofsupernatant and flocculate by centrifugation produces a precipitateenriched with the largest crystallites in the sample. This procedure canbe repeated until no further sharpening of the optical absorptionspectrum is noted. Size-selective precipitation can be carried out in avariety of solvent/nonsolvent pairs, including pyridine/hexane andchloroform/methanol. The size-selected nanocrystal population preferablyhas no more than a 15% rms deviation from mean diameter, more preferably10% rms deviation or less, and most preferably 5% rms deviation or less.

Transmission electron microscopy (TEM) can provide information about thesize, shape, and distribution of the semiconductor nanocrystalpopulation. Powder X-ray diffraction (XRD) patterns can provide the mostcomplete information regarding the type and quality of the crystalstructure of the semiconductor nanocrystals. Estimates of size are alsopossible since particle diameter is inversely related, via the X-raycoherence length, to the peak width. For example, the diameter of thesemiconductor nanocrystal can be measured directly by transmissionelectron microscopy or estimated from X-ray diffraction data using, forexample, the Scherrer equation. It also can be estimated from the UV/Visabsorption spectrum.

As discussed herein, nanocrystals preferably have ligands attachedthereto.

In preparing a shell, ligands can, for example, be derived from thesolvent used during the growth process. The surface can be modified byrepeated exposure to an excess of a competing coordinating group to forman overlayer. For example, a dispersion of the capped nanocrystal can betreated with a coordinating organic compound, such as pyridine, toproduce nanocrystals which disperse readily in pyridine, methanol, andaromatics but no longer disperse in aliphatic solvents. Such a surfaceexchange process can be carried out with any compound capable ofcoordinating to or bonding with the outer surface of the nanocrystal,including, for example, phosphines, thiols, amines and phosphates. Thenanocrystal can be exposed to short chain polymers which exhibit anaffinity for the surface and which terminate in a moiety having anaffinity for a liquid medium in which the nanocrystal is suspended ordispersed. Such affinity improves the stability of the suspension anddiscourages flocculation of the nanocrystal.

Organic ligands can be useful in facilitating large area, non-epitaxialdeposition of highly stable inorganic nanocrystals within a device.

In certain embodiments, a coordinating ligand can have the formula:(Y—)_(k-n)—(X)-(-L)_(n)wherein k is 2, 3 4, or 5, and n is 1, 2, 3, 4 or 5 such that k-n is notless than zero; X is O, O—S, O—Se, O—N, O—P, O—As, S, S═O, SO2, Se,Se═O, N, N═O, P, P═O, C═OAs, or As═O; each of Y and L, independently, isH, OH, aryl, heteroaryl, or a straight or branched C2-18 hydrocarbonchain optionally containing at least one double bond, at least onetriple bond, or at least one double bond and one triple bond. Thehydrocarbon chain can be optionally substituted with one or more C1-4alkyl, C2-4 alkenyl, C2-4 alkynyl, C1-4 alkoxy, hydroxyl, halo, amino,nitro, cyano, C3-5 cycloalkyl, 3-5 membered heterocycloalkyl, aryl,heteroaryl, C1-4 alkylcarbonyloxy, C1-4 alkyloxycarbonyl, C1-4alkylcarbonyl, or formyl. The hydrocarbon chain can also be optionallyinterrupted by —O—, —S—, —N(Ra)—, —N(Ra)—C(O)—O—, —O—C(O)—N(Ra)—,—N(Ra)—C(O)—N(Rb)—, —O—C(O)—O—, —P(Ra)—, or —P(O)(Ra)—. Each of Ra andRb, independently, is hydrogen, alkyl, alkenyl, alkynyl, alkoxy,hydroxylalkyl, hydroxyl, or haloalkyl. An aryl group is a substituted orunsubstituted aromatic group. Examples include phenyl, benzyl, naphthyl,tolyl, anthracyl, nitrophenyl, or halophenyl. A heteroaryl group is anaryl group with one or more heteroatoms in the ring, for instance furyl,pyridyl, pyrrolyl, phenanthryl.

Monodentate alkyl phosphines (and phosphine oxides, the term phosphinein the following discussion of ligands will refer to both) can passivatenanocrystals efficiently. When nanocrystals with conventionalmonodentate ligands are diluted or embedded in a non-passivatingenvironment (i.e. one where no excess ligands are present), they canlose their high luminescence and their initial chemical inertness.Typical are an abrupt decay of luminescence, aggregation, and/or phaseseparation. In order to overcome these possible limitations, polydentateligands can be used, such as a family of polydentate oligomerizedphosphine ligands. The polydentate ligands show a high affinity betweenligand and nanocrystal surface. In other words, they are strongerligands, as is expected from the chelate effect of their polydentatecharacteristics.

Oligomeric phosphines have more than one binding site to the nanocrystalsurface, which ensures their high affinity to the nanocrystal surface.See, for example, for example, U.S. Ser. No. 10/641,292, filed Aug. 15,2003, and U.S. Ser. No. 60/403,367, filed Aug. 15, 2002, each of whichis incorporated by reference in its entirety. The oligomeric phosphinecan be formed from a monomeric, polyfunctional phosphine, such as, forexample, trishydroxypropylphosphine, and a polyfunctionaloligomerization reagent, such as, for example, a diisocyanate. Theoligomeric phosphine can be contacted with an isocyanate of formulaR′-L-NCO, wherein L is C₂-C₂₄ alkylene, and R′ has the formula

R′ has the formula

wherein R^(a) is hydrogen or C₁-C₄ alkyl, or R′ is hydrogen.

A suitable coordinating ligand can be purchased commercially or preparedby ordinary synthetic organic techniques, for example, as described inJ. March, Advanced Organic Chemistry, which is hereby incorporated byreference in its entirety.

Other ligands are described in U.S. patent application Ser. No.10/641,292 for “Stabilized Semiconductor Nanocrystals”, filed 15 Aug.2003, which is hereby incorporated herein by reference in its entirety.

In accordance with one aspect of the invention, there is provided amethod for preparing a nanocrystal comprising a semiconductor materialcomprising one or more elements of Group IIIA of the Periodic Table ofElements and one or more elements of Group VA of the Periodic Table ofElements, the method comprising dispersing one or more Group IIIAprecursors in a first solvent to form one or more Group IIIA reactants;dispersing one or more Group VA precursors in a second solvent to formone or more Group VA reactants; mixing the one or more Group IIIAreactants and the one or more Group VA reactants to form a reactionmixture, and adding an acid to the reaction mixture to promote reactionof the reactants to form nanocrystals of the semiconductor material.Optionally, an amine is also present in the reaction mixture prior tothe addition of the acid. Preferably the acid is dispersed or dissolvedin a third solvent prior to addition. In certain preferred embodiments,the second and third solvents comprises squalane, octadecane, or anothernon-coordinating solvent; and the first solvent comprises methylmyristate, an ether (e.g., dioctyl ether or other high boiling pointethers (see above)), biphenyl, diphenyl oxide, mixtures of two or morecoordinating solvents (e.g., a mixture, more preferably a eutecticmixture of biphenyl and diphenyl oxide (such as, e.g., Dowtherm A)).

In certain preferred embodiments, the ratio of the molar amount of GroupIIIA precursors to the molar amount of Group VA precursors included inthe reaction mixture at the initiation of the reaction is greater thanone. In certain more preferred embodiments this molar ratio is about 2.In certain embodiments, additional Group IIIA and/or Group VA precursorscan be added after nucleation of the nanocrystals.

In certain preferred embodiments, the ratio of the molar amount of H+ tothe molar amount of amine groups included in the reaction mixture at theinitiation of the reaction is greater than one. In certain morepreferred embodiments this molar ratio is about 2.5.

In certain preferred embodiments, the reaction is carried out at aninjection temperature less than 280 C. Preferably, the reactioninjection temperature is in a range from about 175 C to about 260 C,more preferably in a range from about 220 C to about 260 C.

In certain preferred embodiments, the reaction is carried out at agrowth temperature less than 250 C. Preferable, the reaction growthtemperature is in a range from about 170 C to about 225 C, morepreferably in a range from about 175 C to about 205 C.

In certain embodiments, the concentration of Group IIIA precursor in theinjection solution is in a range from about 0.1M to 0.5M, preferable ina range of about 0.2M to 0.3M, and more preferably about 0.25M.

In certain embodiments, the concentration of Group VA precursor in theinjection solution is in a range from about 0.05M to 0.25M, preferablein a range of about 0.1M to 0.15M, and more preferably about 0.125M.

In certain embodiments, the concentration of Group IIIA precursor in thetotal reaction volume is in a range of about 0.02M to 0.1M, preferablein a range of about 0.04M to 0.06M, and more preferably about 0.05M.

In certain embodiments, the concentration of Group VA precursor in thetotal reaction volume is in a range of about 0.01M to 0.05M, preferablein a range of about 0.02M to 0.03M, and more preferably about 0.025M.

In certain embodiments, the concentration of the acid in the totalreaction volume is in a range of about 0.05M to 0.2M, and morepreferably about 0.125M to 0.175M.

In certain embodiments, the concentration of the amine in the totalreaction volume is in a range of about 0.015M to 0.125M, and morepreferably about 0.045M to 0.075M. Preferably the acid comprises acarboxylic acid. Examples of certain preferred embodiments include, butare not limited to, CH₃(CH₂)_(n)C(O)OH wherein n=6-18 (e.g., octanoic[caprylic] acid, nonanoic [pelargonic] acid, decanoic [capric] acid,undecanoic acid, dodecanoic [lauric] acid, tridecanoic acid,tetradecanoic [myristic] acid, pentadecanoic acid, hexadecanoic[palmitic] acid, heptadecanoic [margaric] acid, octadecanoic [stearic]acid, nonadecanoic acid, eicosanoic [arachidic] acid), and mixtures ofany two or more of the foregoing). Other non-limiting examples include9-octadecenoic [oleic] acid. Other suitable acids can be readilyascertained by one of ordinary skill in the art. In certain embodiments,the acid can also act as a ligand source.

In accordance with one aspect of the present invention, a nanocrystalcomprising a semiconductor material comprising one or more elements ofGroup IIIA of the Periodic Table of Elements and one or more elements ofGroup VA of the Periodic Table of Elements is prepared by a methodcomprising dispersing or dissolving one or more Group IIIA precursors ina first solvent to form one or more Group IIIA reactants; dispersing ordissolving one or more Group VA precursors in a second solvent to formone or more Group VA reactants; and reacting one or more Group IIIAreactants with one or more Group VA reactants in a reaction mediumincluding a ligand source to form nanocrystals of the semiconductormaterial having one or more ligands attached to at least a portion ofthe nanocrystals.

In one embodiment, the method comprises dispersing or dissolving one ormore Group IIIA precursors in a first solvent to form one or more GroupIIIA reactants; dispersing or dissolving one or more Group VA precursorsin a second solvent to form one or more Group VA reactants; adding oneor more Group IIIA reactants and one or more Group VA reactants to areaction medium including a third solvent and a ligand source to form areaction mixture, and reacting the reaction mixture under conditionssufficient to form nanocrystals of the semiconductor material having apredetermined composition, predetermined size, and predeterminedemission characteristics, at least a portion of the nanocrystalsincluding one or more ligands attached thereto.

In the various methods of the invention, the relative amounts of the oneor more Group IIIA reactants and the one or more Group VA that arereacted are selected based upon the predetermined composition,predetermined size, and predetermined emission characteristics of thedesired nanocrystal.

Examples of Group IIIA precursors useful in the methods of the inventioninclude elements, covalent compounds, or ionic compounds, includingcoordination complexes or a metal salt, that serve as a source for theelectropositive element or elements in the resulting nanocrystal.Examples of Group VA precursors include elements, covalent compounds, orionic compounds that serve as a source for the electronegative elementor elements in the resulting nanocrystal. In certain embodiments, binarymaterials, ternary materials, quaternary materials, and even morecomplex species may be prepared using the method, in which case morethan one Group IIIA precursor and/or more than one Group VA precursorare included.

For example, a Group IIIA precursor can constitute a wide range ofsubstances, such as a metal oxide, a metal carbonate, a metalbicarbonate, a metal sulfate, a metal sulfite, a metal phosphate, metalphosphite, a metal halide, a metal carboxylate, a metal alkoxide, ametal thiolate, a metal amide, a metal imide, a metal alkyl, a metalaryl, a metal coordination complex, a metal solvate, a metal salt, andthe like. In a typical preparation, the ligand is selected from fattyacids, amines, phosphines, phosphine oxides, or phosphonic acids.Non-limiting examples of indium precursors include InMe₃, In(III)acetate, In(III) trifluoroacetate, InR₃ (wherein R=ethyl, propyl, butyl,pentyl, hexyl, isopropyl, isobutyl, tert-butyl).

Group VA precursors useful in the methods of invention are most oftenselected from the element itself (oxidation state 0), covalentcompounds, or ionic compounds of the group V elements (N, P, As, or Sb).Non-limiting examples of phosphorus precursors include P(SiR₃)₃ whereinR=methyl, ethyl, propyl, butyl, pentyl, hexyl, isopropyl, isobutyl,tert-butyl.

In a typical preparation including a ligand source, the ligand isselected from fatty acids, amines, phosphines, phosphine oxides, orphosphonic acids.

In certain embodiments, the ligand source preferably comprisescarboxylic acids. In certain preferred embodiments, the ligand comprisesCH₃(CH₂)_(n)C(O)OH wherein n=6-18 (e.g., octanoic [caprylic] acid,nonanoic [pelargonic] acid, decanoic [capric] acid, undecanoic acid,dodecanoic [lauric] acid, tridecanoic acid, tetradecanoic [myristic]acid, pentadecanoic acid, hexadecanoic [palmitic] acid, heptadecanoic[margaric] acid, octadecanoic [stearic] acid, nonadecanoic acid,eicosanoic [arachidic] acid). As between myristic acid and stearic acid,myristic acid is preferred. Oleic acid is another example of a preferredacid.

In certain embodiments of method of the invention, the reaction mediumor reaction mixture further includes an amine. Examples of aminesinclude, but are not limited to, secondary amines, e.g.,(CH₃(CH₂)_(n))₂NH wherein n=3-11 (e.g., dibutylamine, dipentylamine,dihexylamine, diheptylamine, dioctylamine, dinonylamine, didecylamine,didundecylamine, didodecylamine), etc.; and primary amines, e.g.,CH₃(CH₂)_(n)NH₂ wherein n=5-19 (e.g., hexylamine, heptylamine,octylamine, nonylamine, decylamine, undecylamine, dodecylamine,tridecylamine, tetradecylamine, pentadecylamine, hexadecylamine,heptadecylamine, octadecylamine, nonadecylamine, eicosylamine). Examplesof preferred amines include octadecylamine and oleylamine. Othersuitable amines can be readily ascertained by one of ordinary skill inthe art.

In certain embodiments, the reaction is carried out in an inertatmosphere, where exposure to air is substantially, and preferablycompletely, precluded.

Examples of suitable coordinating solvents include, but are not limitedto, octadecene, squalene, methyl myristate, octyl octanoate, hexyloctanoate, and CH₃(CH₂)_(n)C(O)O(CH₂)_(m)CH₃ wherein n=4-18 and m=1-8,dioctyl ether, and diphenyl ether, and mixtures of one or more solvents.A preferred mixture comprises a mixture, more preferably a eutecticmixture, of biphenyl and diphenyl oxide, including, e.g., DOWTHERM A,available from the Dow Chemical Company. Other high boiling point ethers(e.g., BP>˜200° C.) may also be used. Such ethers (coordinating) can bearomatic ethers, aliphatic ethers or aromatic aliphatic ethers. Examplesof additional ethers include, but are not limited to, dihexyl ether,diethyleneglycol dimethyl ether, diethyleneglycol dibutyl ether,triethyleneglycol dimethyl ether, tetraethyleneglycol dimethyl ether,butyl phenyl ether, benzyl phenyl ether, dibenzyl ether, ditolyl etherand isomers thereof. Mixtures of two or more solvents can also be used.Other suitable coordinating solvents can be readily ascertained by oneof ordinary skill in the art.

Examples of suitable non-coordinating solvents include, but are notlimited to, squalane, octadecane, or any other saturated hydrocarbonmolecule. Mixtures of two or more solvents can also be used. Othersuitable non-coordinating solvents can be readily ascertained by one ofordinary skill in the art. In certain embodiments, non-coordinatingsolvents comprise liquids having a dipole moment in the range form 0 toabout 0.2 μ/D. In certain embodiments, coordinating solvents compriseliquids having a dipole moment from 0.7 to 4 μ/D (e.g., stronglycoordinating) or liquids having a dipole moment in the range from 0.2 to0.7 μ/D (e.g., weakly coordinating).

In embodiments of methods of the invention including an acid or acidligand source, at higher acid concentrations in the reaction medium orreaction mixture, a larger size distribution may result.

In certain embodiments of methods of the invention that include an acidor acid ligand source and amine in the reaction medium or reactionmixture, increasing the ratio of acid concentration to amineconcentration can provide a nanocrystal capable of emission at higheremission wavelengths and, with 175° C. mixing temperatures, lower FWHMat such higher emission wavelengths.

In certain embodiments, the methods of the invention further includeforming a shell comprising one or more additional semiconductormaterials over at least a portion of the surface of at least a portionof the nanocrystal. In certain preferred embodiments, the one or moreadditional semiconductor materials are different from the semiconductormaterial included in the nanocrystal. Examples of preferredsemiconductor materials for inclusion in the shell include, withoutlimitation, ZnSe and/or ZnS. A more preferred semiconductor material forinclusion in the shell includes ZnSe_(x)S_(1-x) (wherein 0<x<1); mostpreferably x is approximately 0.5. Preferred shell precursor materialsinclude, without limitation, organometallic zinc compounds (e.g.,diethyl zinc), bis-(trialkylsilyl)sulfides, and trialkylphosphineselenides. Other precursors can be readily ascertained by one ofordinary skill in the relevant art.

Preferably the shell is formed at a temperature in a range from about180° C. to about 275° C., more preferably from about 200° C. to about225° C.

When the addition of shell precursors is complete, the overcoatednanocrystals are preferably annealed prior to crash-out (e.g.,precipitation from the reaction mixture) e.g., at a temperature in arange from about 100 C to about 180 C, and more preferably at about 150°C., for at least one hour, and preferably about 12-18 hours. Morepreferably, the annealing is carried out under N₂ atmosphere.

In certain embodiments, the nanocrystal is isolated from the reactionmixture and purified before the shell is formed.

In certain embodiments, a nanocrystal including a shell further includesone or more ligands attached to the surface of the nanocrystal.

EXAMPLES

The examples provided herein are provided as examples and notlimitations, wherein a number of modifications of the exemplifiedcompositions and processes are contemplated and within the scope of thepresent invention.

Example 1 InP Nanocrystal Preparation

FW Moles Amt Compound CAS # (g/mol) (mmol) Equiv. Used myristic acid544-63-8 228.37 2.25 3.00 514 mg dioctylamine 1120-48-5 241.46 0.8821.18 213 mg trimethyl- 3385-78-2 159.93 0.750 1.00 120 mg indium tris-15573-38-3 250.54 0.38 0.50 94 mg trimethyl- silylphos- phine methyl124-10-7 242.41 10 + 4 + 4 mL myristate

Trimethylindium (InMe₃) (Strem Chemicals) is used without furtherpurification. Methyl myristate and dioctylamine (Aldrich) are distilledunder vacuum prior to use. tris-Trimethylsilylphosphine (P(SiMe₃)₃)(Acros or Strem) is distilled under vacuum prior to use. Myristic acid(Aldrich) is used without further purification. n-Hexane, methanol andn-butanol (anhydrous grade) (Aldrich) are used without furtherpurification. Standard glove box and Schlenk techniques are used unlessotherwise noted.

In the glove box, myristic acid and dioctylamine are suspended in 10.0mL of methyl myristate and loaded into a 20 mL septum capped vialequipped with a stirbar. The vial is removed from the box and heated at70° C. under N₂ until all the solids are dissolved forming the ligandsolution. The ligand solution is added by syringe into a preheated,evacuated 4-neck, 50 mL round bottom flask. (The setup includes a4-neck, 50 mL round bottom flask equipped with a stir bar, thermocoupletemperature probe, condenser w/ N₂/vacuum inlet/outlet, and septa on thetwo remaining necks. All connections are standard 14/20 ground glassjoints lubricated with silicone grease—except septa, which are securedwith copper wire. The flask is heated with a heating mantle connected toa digital temperature controller.) The reaction medium is degassed at70° C. for 45-60 minutes and then placed under an N₂ atmosphere andheated to the injection temperature of 260-270° C.

InMe₃ and P(SiMe₃)₃ are weighed out into separate vials in the glove boxand each is separately dissolved in 4.0 mL of methyl myristate. Eachprecursor solution is loaded into a plastic syringe and removed from theglove box. Each precursor syringe is equipped with a 16 gauge, stainlesssteel needle and solutions are rapidly and simultaneously added bysyringe into the heated pot including the reaction medium. Thetemperature drops to ˜185° C. upon injection and is stabilized to200-210° C. by the temperature controller for growth. Upon injection,reaction mixture changes from a colorless solution to a deep red color.

After 5 min at 200-210° C., the reaction mixture is rapidly cooled (<1min) to room temperature with an ice bath. Quality of material isascertained by UV-Vis and Photoluminescence (PL) spectroscopy. TypicalPL values of the material in n-hexane give an emission peak at 585-600nm with a full-width half-maximum (FWHM) of 58-63 nm.

The reaction mixture (including crude InP formed in the presence of theligand source (myristic acid)) is then added by syringe into anevacuated, septum capped vial for transport into the glove box. Thereaction mixture including crude InP is diluted with 5 mL n-hexane and 1mL n-butanol. Methanol is slowly added to the mixture until the reactionbecomes slightly turbid (typically 3-5 mL). The reaction mixture iscentrifuged (4000 rpm, 5 min) and the InP nanocrystals are isolated bydecanting the growth solution. InP is dissolved in ˜3 mL n-hexane(forming a deep red solution) and filtered through a 0.2 μm syringefilter. 100-fold dilutions of the isolated nanocrystals give typical PLspectra with emission=600-610 nm and FWHM=48-52 nm and UV-Vis with anoptical density @350 nm≈0.25. Higher optical densities (greater yields)can be obtained by adding more methanol than described, giving a hardercrash-out (e.g., non-size selective precipitation) and a broader sizedistribution.

Example 2 InP Nanocrystal Preparation

FW Moles Amt Compound CAS # (g/mol) (mmol) Equiv. Used myristic acid544-63-8 228.37 2.25 3.00 514 mg dioctylamine 1120-48-5 241.46 0.8901.19 215 mg trimethyl- 3385-78-2 159.93 0.750 1.00 120 mg indium tris-15573-38-3 250.54 0.38 0.50 94 mg trimethyl- silylphos- phine squalane111-01-3 422.81 9 + 3 mL methyl 124-10-7 242.41 3 mL myristate

InMe₃ (Strem Chemicals) is used without further purification. Methylmyristate and dioctylamine (Aldrich) are distilled under vacuum prior touse. P(SiMe₃)₃ (Acros or Strem) is distilled under vacuum prior to use.Squalane (Aldrich) is degassed in vacuo at 150° C. for 8 h prior to use.Myristic acid (Aldrich) is used without further purification. n-Hexane,methanol and n-butanol (anhydrous grade) (Aldrich) are used withoutfurther purification. Standard glove box and Schlenk techniques are usedunless otherwise noted.

In the glove box, myristic acid and dioctylamine are suspended in 9.0 mLof squalane and loaded into a 20 mL septum capped vial equipped with astirbar. The vial is removed from the box and heated at 70° C. under N₂until all the solids are dissolved to form a ligand solution. The ligandsolution is added by syringe into a preheated, evacuated 4-neck, 50 mLround bottom flask. (The setup includes a 4-neck, 50 mL round bottomflask equipped with a stir bar, thermocouple temperature probe,condenser w/ N₂/vacuum inlet/outlet, and septa on the two remainingnecks. All connections are standard 14/20 ground glass joints lubricatedwith silicone grease—except septa, which are secured with copper wire.The flask is heated with a heating mantle connected to a digitaltemperature controller.) The reaction medium is degassed at 70° C. forapproximately 60 minutes and then placed under an N₂ atmosphere andheated to the injection temperature of 260° C.

InMe₃ is weighed out in the glove box and dissolved in 3.0 mL methylmyristate forming the indium precursor solution. P(SiMe₃)₃ is weighedout in the glove box and dissolved in 3.0 mL squalane forming thephosphorus precursor. Each precursor solution is loaded into a plasticsyringe and removed from the glove box. Each precursor syringe isequipped with a 16 gauge, stainless steel needle and solutions arerapidly and simultaneously added by syringe into the heated potincluding the reaction medium. The temperature drops to ˜210° C. uponinjection and is stabilized to 202-208° C. by the temperature controllerfor growth. Upon injection, reaction mixture changes from a colorlesssolution to a deep red color.

Aliquots of the reaction mixture are removed and analyzed at regularintervals using UV-Vis and PL spectroscopy to monitor reaction progress.After 10-15 min at 202-208° C., reaction mixture is rapidly cooled (<1min) to room temperature with an ice bath. Quality of material isascertained by UV-Vis and Photoluminescence (PL) spectroscopy. TypicalPL values of the material in n-hexane give an emission peak at 565-585nm with a full-width half-maximum (FWHM) of 48-58 nm.

The reaction mixture (including crude InP formed in the presence of theligand source (myristic acid)) is then added by syringe into anevacuated, septum capped vial for transport into the glove box. Thereaction mixture including crude InP is diluted with 5 mL n-hexane and 1mL n-butanol. Acetone is slowly added to the mixture until the reactionbecomes slightly turbid (typically 10-15 mL). The reaction mixture iscentrifuged (4000 rpm, 5 min) and the InP nanocrystals are isolated bydecanting the growth solution. InP is dissolved in ˜3 mL n-hexane(forming a deep red solution) and filtered through a 0.2 μm syringefilter. 100-fold dilutions of the isolated nanocrystals give typical PLspectra with emission=575-595 and FWHM=41-48 nm and UV-Vis with anoptical density @350 nm≈0.25. Higher optical densities (greater yields)can be obtained by adding more methanol than described, giving a hardercrash-out and a broader size distribution.

Example 3 InP Nanocrystal Preparation

FW Moles Amt Compound CAS# (g/mol) (mmol) Equiv. Used myristic acid544-63-8 228.37 2.25 3.00 514 mg dioctylamine 1120-48-5 241.46 0.8901.19 215 mg trimethyl- 3385-78-2 159.93 0.750 1.00 120 mg indium tris-15573-38-3 250.54 0.38 0.50 94 mg trimethyl- silylphos- phine squalane111-01-3 422.81 9 + 3 mL octyl ether 629-82-3 242.44 3 mL

InMe₃ (Strem Chemicals) is used without further purification. Octylether and dioctylamine (Aldrich) are distilled under vacuum prior touse. P(SiMe₃)₃ (Acros or Strem) is distilled under vacuum prior to use.Squalane (Aldrich) is degassed in vacuo at 150° C. for 8 h prior to use.Myristic acid (Aldrich) is used without further purification. n-Hexane,methanol and n-butanol (anhydrous grade) (Aldrich) are used withoutfurther purification. Standard glove box and Schlenk techniques are usedunless otherwise noted.

In the glove box, myristic acid and dioctylamine are suspended in 9.0 mLof squalane and loaded into a 20 mL septum capped vial equipped with astirbar. The vial is removed from the box and heated at 70° C. under N₂until all the solids are dissolved to form a ligand solution. The ligandsolution is added by syringe into a preheated, evacuated 4-neck, 50 mLround bottom flask. (The setup includes a 4-neck, 50 mL round bottomflask equipped with a stir bar, thermocouple temperature probe,condenser w/ N₂/vacuum inlet/outlet, and septa on the two remainingnecks. All connections are standard 14/20 ground glass joints lubricatedwith silicone grease—except septa, which are secured with copper wire.The flask is heated with a heating mantle connected to a digitaltemperature controller.) The reaction medium is degassed at 70° C. forapproximately 60 minutes and then placed under an N₂ atmosphere andheated to the injection temperature of 240° C.

InMe₃ is weighed out in the glove box and dissolved in 3.0 mL octylether forming the indium precursor solution. P(SiMe₃)₃ is weighed out inthe glove box and dissolved in 3.0 mL squalane forming the phosphorusprecursor. Each precursor solution is loaded into a plastic syringe andremoved from the glove box. Each precursor syringe is equipped with a 16gauge, stainless steel needle and solutions are rapidly andsimultaneously added by syringe into the heated pot including thereaction medium. The temperature drops to ˜190° C. upon injection and isstabilized to 177-183° C. by the temperature controller for growth. Uponinjection, reaction mixture changes from a colorless solution to a deepred color.

Aliquots of the reaction mixture are removed and analyzed at regularintervals using UV-Vis and photoluminescence spectroscopy to monitorreaction progress. After approximately 40 min at 177-183° C., reactionmixture is rapidly cooled (<1 min) to room temperature with an ice bath.Quality of material is ascertained by UV-Vis and Photoluminescence (PL)spectroscopy. Typical PL values of the material in n-hexane give anemission peak at 565-585 nm with a full-width half-maximum (FWHM) of48-55 nm.

The reaction mixture (including crude InP formed in the presence of theligand source (myristic acid)) is then added by syringe into anevacuated, septum capped vial for transport into the glove box. Thereaction mixture including crude InP is diluted with 5 mL n-hexane and 1mL n-butanol. Acetone is slowly added to the mixture until the reactionbecomes slightly turbid (typically 10-15 mL). The reaction mixture iscentrifuged (4000 rpm, 5 min) and the InP nanocrystals are isolated bydecanting the growth solution. InP is dissolved in ˜3 mL n-hexane(forming a deep red solution) and filtered through a 0.2 μm syringefilter. 100-fold dilutions of the isolated nanocrystals give typical PLspectra with emission=575-595 and FWHM=41-48 nm and UV-Vis with anoptical density @350 nm≈0.25. Higher optical densities (greater yields)can be obtained by adding more methanol than described, giving a hardercrash-out and a broader size distribution.

Example 4 Overcoating InP Nanocrystals with ZnSe

FW Moles Amt Compound CAS # (g/mol) (mmol)* Used* Diethylzinc 557-20-0123.51 1.16 143 mg Trioctylphosphine 20612-73-1 449.60 1.16 1.16 mLselenide (1M in TOP) Oleylamine 112-90-3 267.49 6.08 2.0 mL 1-octadecene112-88-9 252.48 5.0 mL (ODE) methyl 124-10-7 242.41 5.0 mL myristate*amounts vary depending on optical density of InP core solution used

ZnEt₂ (Strem Chemicals) is filtered through a 0.2 μm syringe filterprior to use. Methyl myristate (Aldrich) is distilled under vacuum priorto use. 1-Octadecene (ODE) (Aldrich) is degassed at 150° C. under vacuumfor several hours prior to use. n-Hexane, methanol and n-butanol(anhydrous grade) (Aldrich) are used without further purification.Oleylamine (Pfalz and Bauer) is distilled under vacuum prior to use.Trioctylphosphine selenide (TOP-Se) is synthesized by dissolving theappropriate amount of selenium shot into trioctylphosphine (TOP).Selenium and TOP (Strem) are used without further purification. Standardglove box and Schlenk techniques are used unless otherwise noted.

Methyl myristate and ODE are added by syringe into a preheated,evacuated 4-neck, 50 mL round bottom flask. (The setup included 4-neck,50 mL round bottom flask equipped with a stir bar, thermocoupletemperature probe, condenser w/ N₂/vacuum inlet/outlet, and septa on thetwo remaining necks. All connections are standard 14/20 ground glassjoints lubricated with silicone grease—except septa, which are securedwith copper wire. The flask is heated with a heating mantle connected toa digital temperature controller.) The reaction medium is degassed at70° C. for 60 minutes and is then placed under an N₂ atmosphere.

Typical preparations involve using a 3.0 mL n-hexane solution of InPnanocrystals (where the 100-fold dilution has an optical density of 0.5@350 nm).

The InP solution is prepared in the glove box and added by syringe intothe pot containing the degassed solvent. n-Hexane is removed in vacuo(˜30 minutes) and the flask is placed back under N₂ and heated to 200°C. TOP-Se and diethylzinc are measured out into separate vials in theglove box and are dissolved in ODE and diluted such that each has atotal volume of 4.0 mL. The solutions are loaded into two 5 mL syringesand removed from the glove box. Se and Zn solutions are added slowly tothe pot using a syringe pump and capillary tubing. Upon starting thesyringe pump, 2.0 mL of oleylamine is rapidly injected into the flaskcontaining the InP solution. Typical addition time of the zinc andselenium reagents is 2 h using an addition rate of 33 μL/min (2 mL/h).After Zn and Se precursor addition is completed, reaction mixture isallowed to slowly cool to ca. 70° C. over a course of 30 min.

The reaction is then added by syringe into an evacuated, septum cappedvial for transport into the glove box. Upon cooling, a flocculent, whitesolid precipitates out of the red reaction mixture. The reaction mixtureis reheated to ca. 70° C. to redissolve the white solid, forming a red,homogenous solution. The mixture is diluted with 10 mL n-hexane andcentrifuged (4000 rpm for 5 min). The red supernatant is decanted andcollected and the white solids are washed with n-hexane (˜10 mL) andcentrifuged again. The supernatant is decanted off and added to thefirst fraction. ˜5 mL of n-butanol is added to the red nanocrystalsolution followed by enough methanol to make the solution turbid(typically ˜10 mL). If phase separation occurs, n-butanol is added in 1mL increments until the mixture is homogenous. The turbid solution isthen centrifuged and the supernatant is decanted and discarded. Thereddish-brown solid left behind is dissolved in ˜5 mL n-hexane andfiltered through a 0.2 μm syringe filter. Typical photoluminescencespectra give emission of 615±10 nm with a FWHM=60±5 nm.

Following is a table of data (peak emission (nm), width of the emissionpeak at half of the maximum peak height (FWHM) (nm), andphotoluminescence quantum efficiency (PLQE) (measured vs. cresylviolet)) measurements for various ZnSe overcoated InP samples. (The InPcores and ZnSe shells of a given sample were generally preparedaccording to the procedure set forth in the Examples referenced for thegiven sample.)

Example 5 Overcoating InP Nanocrystals with ZnSe_(x)S_(1-x)

FW Moles Amt Compound CAS # (g/mol)* (mmol)* Used diethylzinc 557-20-0123.51 1.79 221 mg trioctylphosphine 20612-73-1 449.60 0.89 0.89 mLselenide (1M in TOP) bis-(trimethylsilyl) 3385-94-2 178.44 1.79 319 mgsulfide oleylamine 112-90-3 267.49 6.08 2.0 mL 1-octadecene (ODE)112-88-9 252.48 5.0 mL methyl 124-10-7 242.41 5.0 mL myristate *amountsvary depending on optical density of InP core solution used

ZnEt₂ (Strem Chemicals) is filtered through a 0.2 μm syringe filterprior to use. Methyl myristate and bis-(trimethylsilyl)sulfide (Aldrich)is distilled under vacuum prior to use. 1-Octadecene (ODE) (Aldrich) isdegassed at 150° C. under vacuum for several hours prior to use.n-Hexane, methanol and n-butanol (anhydrous grade) (Aldrich) are usedwithout further purification. Oleylamine (Pfalz and Bauer) is distilledunder vacuum prior to use. Trioctylphosphine selenide (TOP-Se) issynthesized by dissolving the appropriate amount of selenium shot intotrioctylphosphine (TOP). Selenium and TOP (Strem) are used withoutfurther purification. Standard glove box and Schlenk techniques are usedunless otherwise noted.

Methyl myristate and ODE are added by syringe into a preheated,evacuated 4-neck, 50 mL round bottom flask. (The setup included 4-neck,50 mL round bottom flask equipped with a stir bar, thermocoupletemperature probe, condenser w/ N₂/vacuum inlet/outlet, and septa on thetwo remaining necks. All connections are standard 14/20 ground glassjoints lubricated with silicone grease—except septa, which are securedwith copper wire. The flask is heated with a heating mantle connected toa digital temperature controller.) The reaction medium is degassed at70° C. for 60 minutes and is then placed under an N₂ atmosphere.

Typical preparations involve using a 1.0 mL n-hexane solution of InPnanocrystals (where the 100-fold dilution has an optical density of 1.0@350 nm).

The InP solution is prepared in the glove box and added by syringe intothe pot containing the degassed solvent. n-Hexane is removed in vacuo(˜30 minutes) and the flask is placed back under N₂ and heated to 200°C. TOP-Se and bis-(trimethylsilyl)sulfide are measured out into separatevials in the glove box and are each dissolved in ODE and diluted suchthat each has a total volume of 1.0 mL forming the selenide and sulfideprecursor solutions, respectively. Diethylzinc is dissolved in 2.0 mLODE forming the zinc precursor solution. The precursor solutions areloaded into three 5 mL syringes and removed from the glove box. Selenideand zinc precursor solutions are added slowly to the pot using a syringepump and capillary tubing. Upon starting the syringe pump, 2.0 mL ofoleylamine is rapidly injected into the flask containing the InPsolution. Typical addition time of the zinc and selenium reagents is 1 husing an addition rate of 33 μL/min (2 mL/h). After the 2.0 mL ofselenide precursor has been added, the syringe pump is stopped for tenminutes and the selenide precursor syringe is removed and replaced withthe syringe containing the sulfide precursor solution. The syringe pumpsare restarted and the sulfide precursor solution and remaining zincprecursor solution are added over a period of 1 h. After the zinc andsulfide precursor addition is completed, reaction mixture is allowed toslowly cool to ca. 70° C. over a course of 30 min.

The reaction is then added by syringe into an evacuated, septum cappedvial for transport into the glove box. Upon cooling, a flocculent, whitesolid precipitates out of the red reaction mixture. The reaction mixtureis reheated to ca. 70° C. to redissolve the white solid, forming a red,homogenous solution. The mixture is diluted with 10 mL n-hexane andcentrifuged (4000 rpm for 5 min). The red supernatant is decanted andcollected and the white solids are washed with n-hexane (˜10 mL) andcentrifuged again. The supernatant is decanted off and added to thefirst fraction. ˜5 mL of n-butanol is added to the red nanocrystalsolution followed by enough methanol to make the solution turbid(typically ˜10 mL). If phase separation occurs, n-butanol is added in 1mL increments until the mixture is homogenous. The turbid solution isthen centrifuged and the supernatant is decanted and discarded. Thereddish-brown solid left behind is dissolved in ˜5 mL n-hexane andfiltered through a 0.2 μm syringe filter. Typical photoluminescencespectra give emission of 615±10 nm with a FWHM=60-90 nm.

Following is a table of data (peak emission (nm), width of the emissionpeak at half of the maximum peak height (FWHM) (nm), andphotoluminescence quantum efficiency (PLQE) (measured vs. cresylviolet)) measurements for various ZnSeS overcoated InP samples. (The InPcores and ZnSeS shells of a given sample were generally preparedaccording to the procedure set forth in the Examples referenced for thegiven sample.)

Example 6 Overcoating InP Nanocrystals with ZnSe_(x)S_(1-x)

FW Moles Amt Compound CAS # (g/mol)* (mmol)* Used diethylzinc 557-20-0123.51 1.64 202 mg trioctylphosphine 20612-73-1 449.60 0.82 0.82 mLselenide (1M in TOP) bis-(trimethylsilyl) 3385-94-2 178.44 1.64 292 mgsulfide oleylamine 112-90-3 267.49 6.08 2.0 mL 1-octadecene (ODE)112-88-9 252.48 5.0 mL methyl 124-10-7 242.41 5.0 mL myristate *amountsvary depending on optical density of InP core solution used

ZnEt₂ (Strem Chemicals) is filtered through a 0.2 μm syringe filterprior to use. Methyl myristate and bis-(trimethylsilyl)sulfide (Aldrich)is distilled under vacuum prior to use. 1-Octadecene (ODE) (Aldrich) isdegassed at 150° C. under vacuum for several hours prior to use.n-Hexane, methanol and n-butanol (anhydrous grade) (Aldrich) are usedwithout further purification. Oleylamine (Pfalz and Bauer) is distilledunder vacuum prior to use. Trioctylphosphine selenide (TOP-Se) issynthesized by dissolving the appropriate amount of selenium shot intotrioctylphosphine (TOP). Selenium and TOP (Strem) are used withoutfurther purification. Standard glove box and Schlenk techniques are usedunless otherwise noted.

Methyl myristate and ODE are added by syringe into a preheated,evacuated 4-neck, 50 mL round bottom flask. (The setup included 4-neck,50 mL round bottom flask equipped with a stir bar, thermocoupletemperature probe, condenser w/ N₂/vacuum inlet/outlet, and septa on thetwo remaining necks. All connections are standard 14/20 ground glassjoints lubricated with silicone grease—except septa, which are securedwith copper wire. The flask is heated with a heating mantle connected toa digital temperature controller.) The reaction medium is degassed at70° C. for 60 minutes and is then placed under an N₂ atmosphere.

Typical preparations involve using a 1.0 mL n-hexane solution of InPnanocrystals (where the 100-fold dilution has an optical density of 1.0@350 nm).

The InP solution is prepared in the glove box and added by syringe intothe pot containing the degassed solvent. n-Hexane is removed in vacuo(˜30 minutes) and the flask is placed back under N₂ and heated to 200°C. TOP-Se and bis-(trimethylsilyl)sulfide are measured out into one vialin the glove box and are dissolved in ODE and diluted to a total volumeof 2.0 mL forming the selenide/sulfide precursor solution. Diethylzincis dissolved in 2.0 mL ODE forming the zinc precursor solution. Theprecursor solutions are loaded into two 5 mL syringes and removed fromthe glove box. Selenide/sulfide and zinc precursor solutions are addedslowly to the pot using a syringe pump and capillary tubing. Uponstarting the syringe pump, 2.0 mL of oleylamine is rapidly injected intothe flask containing the InP solution. Typical addition time of the zincand selenide/sulfide reagents is 1 h using an addition rate of 33 μL/min(2 mL/h). After the zinc and selenide/sulfide precursor addition iscompleted, reaction mixture is allowed to slowly cool to ca. 70° C. overa course of 30 min.

The reaction is then added by syringe into an evacuated, septum cappedvial for transport into the glove box. Upon cooling, a flocculent, whitesolid precipitates out of the red reaction mixture. The reaction mixtureis reheated to ca. 70° C. to redissolve the white solid, forming a red,homogenous solution. The mixture is diluted with 10 mL n-hexane andcentrifuged (4000 rpm for 5 min). The red supernatant is decanted andcollected and the white solids are washed with n-hexane (˜10 mL) andcentrifuged again. The supernatant is decanted off and added to thefirst fraction. ˜5 mL of n-butanol is added to the red nanocrystalsolution followed by enough methanol to make the solution turbid(typically ˜10 mL). If phase separation occurs, n-butanol is added in 1mL increments until the mixture is homogenous. The turbid solution isthen centrifuged and the supernatant is decanted and discarded. Thereddish-brown solid left behind is dissolved in ˜5 mL n-hexane andfiltered through a 0.2 μm syringe filter. Typical photoluminescencespectra give emission of 590±10 nm with a FWHM=65±5 nm.

Following is a table of data (peak emission (nm), width of the emissionpeak at half of the maximum peak height (FWHM) (nm), andphotoluminescence quantum efficiency (PLQE) (measured vs. cresylviolet)) measurements for various ZnSeS overcoated InP samples. (The InPcores and ZnSeS shells of a given sample were generally preparedaccording to the procedure set forth in the Examples referenced for thegiven sample.)

Example 7 Overcoating InP Nanocrystals with ZnSe_(x)S_(1-x)

FW Moles Amt Compound CAS # (g/mol)* (mmol)* Used Diethylzinc 557-20-0123.51 1.31 161 mg trioctylphosphine 20612-73-1 449.60 0.65 0.65 mLselenide (1M in TOP) bis-(trimethylsilyl) 3385-94-2 178.44 0.65 117 mgsulfide Oleylamine 112-90-3 267.49 6.08 2.0 mL squalane 111-01-3 422.815.0 mL methyl 124-10-7 242.41 5.0 mL myristate *amounts vary dependingon optical density of InP core solution used

ZnEt₂ (Strem Chemicals) is filtered through a 0.2 μm syringe filterprior to use. Methyl myristate and bis-(trimethylsilyl)sulfide (Aldrich)is distilled under vacuum prior to use. Squalane (Aldrich) is degassedat 150° C. under vacuum for several hours prior to use. n-Hexane,methanol and n-butanol (anhydrous grade) (Aldrich) are used withoutfurther purification. Oleylamine (Pfalz and Bauer) is distilled undervacuum prior to use. Trioctylphosphine selenide (TOP-Se) is synthesizedby dissolving the appropriate amount of selenium shot intotrioctylphosphine (TOP). Selenium and TOP (Strem) are used withoutfurther purification. Standard glove box and Schlenk techniques are usedunless otherwise noted.

Methyl myristate and squalane are added by syringe into a preheated,evacuated 4-neck, 50 mL round bottom flask. (The setup included 4-neck,50 mL round bottom flask equipped with a stir bar, thermocoupletemperature probe, condenser w/ N₂/vacuum inlet/outlet, and septa on thetwo remaining necks. All connections are standard 14/20 ground glassjoints lubricated with silicone grease—except septa, which are securedwith copper wire. The flask is heated with a heating mantle connected toa digital temperature controller.) The reaction medium is degassed at70° C. for 60 minutes and is then placed under an N₂ atmosphere.

Typical preparations involve using a 1.0 mL n-hexane solution of InPnanocrystals (where the 100-fold dilution has an optical density of 1.0@350 nm).

The InP solution is prepared in the glove box and added by syringe intothe pot containing the degassed solvent. n-Hexane is removed in vacuo(˜30 minutes) and the flask is placed back under N₂ and heated to 200°C. TOP-Se and bis-(trimethylsilyl)sulfide are measured out into one vialin the glove box and are dissolved in squalane and diluted to a totalvolume of 2.0 mL forming the selenide/sulfide precursor solution.Diethylzinc is dissolved in 2.0 mL squalane forming the zinc precursorsolution. The precursor solutions are loaded into two 5 mL syringes andremoved from the glove box. Selenide/sulfide and zinc precursorsolutions are added slowly to the pot using a syringe pump and capillarytubing. Upon starting the syringe pump, 2.0 mL of oleylamine is rapidlyinjected into the flask containing the InP solution. Typical additiontime of the zinc and selenide/sulfide reagents is 2 h using an additionrate of 1.00 mL/h. After the zinc and selenide/sulfide precursoraddition is completed, reaction mixture is allowed to slowly cool to ca.70° C. over a course of 30 min.

The reaction is then added by syringe into an evacuated, septum cappedvial for transport into the glove box. Upon cooling, a flocculent, whitesolid precipitates out of the red reaction mixture. The reaction mixtureis reheated to ca. 70° C. to redissolve the white solid, forming a red,homogenous solution. The mixture is diluted with 10 mL n-hexane andcentrifuged (4000 rpm for 5 min). The red supernatant is decanted andcollected and the white solids are washed with n-hexane (˜10 mL) andcentrifuged again. The supernatant is decanted off and added to thefirst fraction. ˜10 mL of n-butanol is added to the red nanocrystalsolution followed by enough methanol to make the solution turbid(typically ˜10 mL). If phase separation occurs, n-butanol is added in 1mL increments until the mixture is homogenous. The turbid solution isthen centrifuged and the supernatant is decanted and discarded. Thereddish-brown solid left behind is dissolved in ˜5 mL n-hexane andfiltered through a 0.2 μm syringe filter. Typical photoluminescencespectra give emission of 600±10 nm with a FWHM=60±5 nm.

The size distribution of InP nanocrystals overcoated withZnSe_(x)S_(1-x) using squalane (as described in Example 7) is narrowerthan that obtained when carrying out the overcoating process using ODE.

Following is a table of data (peak emission (nm), width of the emissionpeak at half of the maximum peak height (FWHM) (nm), andphotoluminescence quantum efficiency (PLQE) (measured vs. cresylviolet)) measurements for various ZnSeS overcoated InP samples. (The InPcores and ZnSeS shells of a given sample were generally preparedaccording to the procedure set forth in the Examples referenced for thegiven sample.)

InP Core InP InP ZnSe Core/Shell InP Prep. Peak Core Core Prep. PeakCore/Shell Core/Shell Method Emission FWHM PLQE Method Emission FWHMPLQE Sample (Example #) (nm) (nm) (%) (Example #) (nm) (nm) (%) A 1 61351 — 4 609 63 31 B 2 578 44 — 5 612 81 36 C 2 573 43 — 6 597 62 39 D 2572 52 — 6 584 63 31 E 2 572 48 — 7 604 55 34

In the foregoing table, the photoluminescence quantum efficiency ismeasured by comparison to cresyl violet (cresyl violet 670 perchlorate,Exciton product #06700) in methanol following the method described byWilliams, et. al. in “Relative fluorescence quantum yields using acomputer controlled luminescence spectrometer,” Analyst, 1983, 108,1067. Cresyl violet, which has a reported quantum yield of 54% asdescribed in J. Phys. Chem., 1979, 83, 696, is used to calculate quantumyields of unknown semiconductor nanocrystal samples in n-hexane bycomparison. A series of UV/Vis and PL spectra are taken for severaldifferent concentrations of cresyl violet in methanol (keeping theoptical density below 0.1 to avoid re-absorption effects, as describedby Dhami, et. al. in “Pthalocyanine fluorescence at high concentration:dimers or reabsorption effect?” Photochem. Photobiol., 1995, 61, 341.).Integrated intensity of fluorescence is plotted vs. absorbance and aregression line is fitted to the curve, giving a straight line thatpasses through the origin and has a slope of m_(standard). The unknownnanocrystal sample in hexane is submitted to the same experiment, i.e.UV/Vis and PL spectra are taken at several concentrations and integratedintensity of fluorescence is plotted vs. absorbance. It is important tonote that the spectra for the standard and the unknown are taken usingroughly the same concentration ranges, over the same spectral range,using the same excitation wavelength, and in general using the exactparameters not explicitly listed here for both unknown and standard(i.e. PL spectrometer slit widths). A regression line is fitted to thecurve from the unknown nanocrystal data giving a straight line thatpasses through the origin with a slope of m_(nanocrystal). Fluorescencequantum yield is calculated using the following equation:Φ_(nanocrystal)=Φ_(standard)*(m _(nanocrystal) /m_(standard))*(η_(nanocrystal) ²/η_(standard) ²)wherein Φ_(standard)=0.54 (quantum yield of cresyl violet),m_(nanocrystal) and m_(standard) are the slopes calculated as describedabove, η_(nanocrystal) is the refractive index of the solvent used tosolvate the nanocrystals (n-hexane, 1.375), and η_(standard) is therefractive index of the solvent used to solvate the cresyl violetstandard (methanol, 1.328).

Example 8 InP Nanocrystal Preparation

A. Preparation of the Flask Solution:

In the glove box, 514 mg (3.0 equivalents) of myristic acid and 215 mg(1.2 equivalents) of amine are weighed out in a septum capped vial.

9 mL of squalane was added to the septum capped vial. The vial wasclosed well, brought out of the glove box and heated to 70° C. in an oilbath under nitrogen atmosphere to dissolve the ligands in squalane.

When the solution became clear after complete dissolution of the ligandsin squalane, the solution is syringed out of the vial and injected intoa preheated, evacuated 4-neck, 50 mL round bottom flask. (Standardindium phosphide setup was used; 4-neck, 50 mL RB was equipped with astir bar, thermocouple temperature probe, condenser w/ N₂/vacuuminlet/outlet, and septa on the remaining necks. All connections werestandard 14/20 ground glass joints lubricated with siliconegrease—except septa, which were secured with copper wire. The flask wasevacuated at 100° C. heated with a heating mantle connected to a digitaltemperature controller.)

The contents were further degassed again at 100° C. for approximately 60minutes. The contents of the ligand solution along with the equivalentsand moles used are given in the table below.

FW moles Compound CAS # (g/mol) (mmol) Equivalents Quantity UnitsMyristic acid 544-63-8 228.37 2.250733459 3.0 497 mg Dioctylamine1120-48-5 241.46 0.890416632 1.2 235 mg Squalane 111-01-3 422.81 Solvent9 mLB. Preparation of Solutions of the Precursors for Injection:In the Glove Box:

120 mg (1 equivalent) of trimethyl indium was dissolved in 3 mL of octylether in a septum capped vial. The solution is then transferred from thevial into a 5 mL syringe fitted with a gauge 12 needle. The syringe tipis then capped by the empty septum capped vial to avoid any aircontamination (when the syringes are brought out of the glove box).

94 mg (0.5 equivalents) of tris-(trimethylsilyl)-phosphine was dissolvedin 3 mL of squalane in another septum capped vial. This solution isagain transferred into a separate 5 mL syringe fitted with a gauge 12needle. The syringe tip is again capped by the empty septum capped vialsimilar to that of the syringe containing trimethyl indium. The reagentsand the solvents used for injection are given in the table below.

Syringe 1:

Com- Moles Equiv- Quan- pound CAS# FW (g/mol) (mmol) alents tity UnitsInMe₃ 15573- 250.54 0.750328269 1 120 mg 38-3 Octyl 629-82- 242.44Solvent 3 mL ether 3Syringe 2:

Moles Compound CAS # FW (g/mol) (mmol) Equivalents Quantity UnitsP(TMS)₃ 15573- 250.54 0.37518959 0.500033927 94 mg 38-3 Squalane111-01-3 422.81 Solvent 3 mL

The reaction flask containing the ligand solution is backfilled withnitrogen and maintained under nitrogen atmosphere. Any deposition ofligand material at the top of the flask was melted down into the flasksolution by gently heating the top outer surface of the flask and thecondenser with a heat gun. The temperature of the flask was then raisedto 260° C.

The vial capped syringes containing the precursor solutions (trimethylindium and tris-(trimethylsilyl)-phosphine) were brought out of theglove box and kept inserted in the septa of the flask (ready forinjection).

When the temperature reaches above 260° C., the temperature of thetemperature controller is reduced to 205° C. When the temperature of theflask drops just to 260° C., the precursor solutions are injectedrapidly from the syringes into the contents of the flask and a stopclock was simultaneously started to monitor the time of the reaction.Due to injection, the temperature generally dropped to 202° C. Duringthe reaction, the temperature of the flask was generally maintainedbetween 202° C. and 210° C.

During the reaction, samples of the reaction mixture are extractedthrough 1 mL syringes fitted with longer needles and analyzed forabsorption and emission wavelengths and the corresponding full widthhalf maximum of the emission wavelength peak using the respective Varianspectrophotometer.

When the emission wavelength reached 574 nm with a full width halfmaximum value of 48 nm, the reaction mixture was cooled rapidly using anice bath to room temperature.

The cooled reaction mixture was then transferred into an evacuatedseptum capped vial using a 20 mL syringe and the septum capped vial wastaken into the glove box to isolate the nanoparticles from the reactionmixture.

C. Preparation of the Ligand Solution:

Myristic Dioctyl Squalane Degassing Degas Acid amine (mg) (ml) time(min) temperature (° C.) 514 215 9 60 100D. Injection Reagents and Injection Conditions:

Post- Injection injection Syringe 1 Syringe 2 Temper- Temper- InMe₃Octyl ether P(TMS)₃ Squalane ature ature (mg) (ml) (mg) (ml) (° C.) (°C.) 120 3 94 3 260 202E. Other Details:

Growth Temperature Reaction (° C.) Time (min) Sampling (minutes)Quenching 205 37 15, 35, 48, 60 Ice bath coolingF. Experimental Results:

Time (min) Absorption (λ) Emission (λ) FWHM (λ) 15 497 542 Broad 35 525561 42 48 533 570 45 60 538 574 48G. Clean Up and Preparation of Red Core Particles:

Inside the glove box, the crude reaction mixture of core nanoparticlesis completely dissolved in about 3 mL of hexanes and transferred into acentrifuge tube.

To this solution, about 20 mL of n-butanol was added. The solutionremains clear at this stage. To this solution, about 19 mL of methanolwas added slowly until the solution becomes turbid.

The turbid solution in the centrifuge tube was centrifuged in acentrifuge for 5 minutes at 4000 revolutions per minute.

After centrifuging, the supernatant solution is discarded and thedeposited core nanoparticles were dissolved in 5 mL of hexanes. The corenanoparticles solution was then transferred into a septum capped vialand stored in the glove box until it is needed for overcoating.

The quantum yield of the core particles after isolation from the crudereaction mixture was found to be 8%.

Example 9 InP Nanocrystal Preparation

A. Preparation of the Flask Solution:

In the glove box, 497 mg (2.9 equivalents) of myristic acid and 235 mg(1.3 equivalents) of amine are weighed out in a septum capped vial.

9 mL of squalane was added to the septum capped vial. The vial wasclosed well, brought out of the glove box and heated to 70° C. in an oilbath under nitrogen atmosphere to dissolve the ligands in squalane.

When the solution became clear after complete dissolution of the ligandsin squalane, the solution was syringed out of the vial and injected intoa preheated, evacuated 4-neck, 50 mL round bottom flask. (Standardindium phosphide setup was used; 4-neck, 50 mL RB was equipped with astir bar, thermocouple temperature probe, condenser w/ N₂/vacuuminlet/outlet, and septa on the remaining necks. All connections werestandard 14/20 ground glass joints lubricated with siliconegrease—except septa, which were secured with copper wire. The flask wasevacuated at 100° C. heated with a heating mantle connected to a digitaltemperature controller.)

The contents were further degassed again at 70° C. for approximately 60minutes. The contents of the ligand solution along with the equivalentsand moles used are given in the table below.

FW moles Compound CAS # (g/mol) (mmol) equiv. Quantity Quantity Myristicacid 544-63-8 228.37 2.175951980 2.9 497 mg Dioctyl amine 1120-48-5241.46 0.975426750 1.3 235 mg Squalane 111-01-3 422.81 Solvent 9 mLB. Preparation of Solutions of the Precursors for Injection:In the Glove Box:

120 mg (1 equivalent) of trimethyl indium was dissolved in 3 mL ofDowtherm A in a septum capped vial. The solution is then transferredfrom the vial into a 5 mL syringe fitted with a gauge 12 needle. Thesyringe tip is then capped by the empty septum capped vial to avoid anyair contamination (when the syringes are brought out of the glove box).

94 mg (0.5 equivalents) of tris-(trimethylsilyl)-phosphine was dissolvedin 3 mL of squalane in another septum capped vial. This solution wasagain transferred into a separate 5 mL syringe fitted with a gauge 12needle. The syringe tip was again capped by the empty septum capped vialsimilar to that of the syringe containing indium phosphide. The reagentsand the solvents used for injection are given in the table below.

Syringe 1:

Moles Compound CAS# FW (g/mol) (mmol) Equivalents Quantity QuantityInMe₃ 15573-38-3 250.54 0.750328269 1 120 mg Dowtherm A 8004-13-5Solvent 3 mLSyringe 2:

Moles Compound CAS # FW (g/mol) (mmol) Equivalents Quantity QuantityP(TMS)₃ 15573-38-3 250.54 0.37518959 0.500033927 94 mg Squalane 111-01-3422.81 Solvent 3 mL

The reaction flask containing the ligand solution is backfilled withnitrogen and maintained under nitrogen atmosphere. Any deposition ofligand material at the top of the flask was melted down into the flasksolution by gently heating the top outer surface of the flask and thecondenser with a heat gun. The temperature of the flask was then raisedto 220° C.

The vial capped syringes containing the precursor solutions (trimethylindium and tris-(trimethylsilyl)-phosphine) were brought out of theglove box and kept inserted in the septa of the flask (ready forinjection).

When the temperature reached above 220° C., the temperature of thetemperature controller was reduced to 175° C. When the temperature ofthe flask drops just to 220° C., the precursor solutions were injectedrapidly from the syringes into the contents of the flask and a stopclock is simultaneously started to monitor the time of the reaction. Dueto injection, the temperature generally dropped to 172° C. During thereaction, the temperature of the flask is generally maintained between172° C. and 180° C.

During the reaction, samples of the reaction mixture are extractedthrough 1 mL syringes fitted with longer needles and analyzed forabsorption and emission wavelengths and the corresponding full widthhalf maximum of the emission wavelength peak using the respective Varianspectrophotometer.

When the emission wavelength reached 558 nm with a full width halfmaximum value of 44 nm, the reaction mixture was cooled rapidly using anice bath to room temperature. The quantum yield of the crude solutionwas found to be 3.8%

The cooled reaction mixture was then transferred into an evacuatedseptum capped vial using a 20 mL syringe and the septum capped vial wastaken into the glove box to isolate the nanoparticles from the crudereaction mixture.

The data observed during the course of the reaction is tabulated belowalong with the vital conditions used for the reaction.

C. Preparation of the Ligand Solution:

Degas Myristic Dioctyl Degassing temperature Acid amine (mg) Squalane(ml) time (min) (° C.) 497 235 9 60 100D. Injection Reagents and Injection Conditions:

Post- Syringe 1 Syringe 2 Injection injection InMe₃ Dowtherm P(TMS)₃Squalane Temperature Temperature (mg) A (ml) (mg) (ml) (° C.) (° C.) 1203 94 3 220 172E. Other Details:

Growth Reaction Temperature (° C.) Time (min) Sampling Quenching 172-18092 10, 20, 35, 50, Ice bath cooling 70, 80, 90, 92F. Experimental Results:

Time (min) Absorption (λ) Emission (λ) FWHM (λ) 10 442 603 Broad 20 449604 Broad 35 464 529/602 Broad 50 484 536 Broad 70 498 543 47 80 507 55348 90 510 558 44 92 515 558 44G. Clean Up and Preparation of Red Core Particles:

Inside the glove box, the crude reaction mixture of core nanoparticleswas completely dissolved in about 3 mL of hexanes and transferred into acentrifuge tube.

To this solution, about 20 mL of n-butanol was added. The solutionremains clear at this stage. To this solution, about 18 mL of methanolis added slowly until the solution becomes turbid.

The turbid solution in the centrifuge tube is centrifuged in acentrifuge for 5 minutes at 4000 revolutions per minute.

After centrifuging, the supernatant solution is discarded and thedeposited core nanoparticles were dissolved in 5 mL of hexanes. The corenanoparticles solution was then transferred into a septum capped vialand stored in the glove box until it is needed for overcoating.

The quantum yield of the core nanoparticles after isolation from thecrude reaction mixture was found to be 4%.

Example 10 Overcoating InP Nanocrystals with ZnSe_(x)S_(1-x)

A. Equivalent Amount of Cores, Reagents and Solvents

CAS FW Moles Amount Compound number (g/mol) (mmol) Used Indium phosphideCore 0.096^(a) Diethylzinc 557-20-0 123.51 1.1^(b) 131 mg/111 ul Bis-3385-94-2 178.44 0.53^(b) 95 mg/112 ul (trimethylsilyl)sulfide 1Mtrioctylphosphine n/a 0.53^(b) 0.53 ml selenide Oleylamine 112-90-3267.49 6.08 2.0 ml Squalane 111-01-3 422.81 9.0 ml Methylmyristate124-10-7 242.41 5.0 ml ^(a)The mole amount of InP is calculated using‘InP-overcoating spreadsheet’, based on the absorption peak wavelengthand the optical density at 350 nm of 100-fold dilution of the InPsolution. The number between 0.070 mmol to 1.2 mmol is acceptable.^(b)The mole amount and ratios vary depending on the amount of InP, anumber of shell layers, and a percentage of sulfur vs. selenium. Thenumbers above mentioned are based on 15 shell layers made up ofZnSe_(0.5)S_(0.5) for InP cores with absorption peak at 513 nm.B. General Preparation

All cores, reagents and solvents are kept in a glove box afterappropriate air-free treatment. Standard glove box and Schlenktechniques are used unless otherwise mentioned. Diethylzinc is filteredthrough a 0.2 μm syringe filter prior to use and kept in freezer. Methylmyristate and oleylamine are distilled under vacuum, and squalane isdegassed under vacuum at high temperature prior to use. 1Mtrioctylphosphine selenide (TOP-Se) is prepared by dissolving seleniumshot in trioctylphosphine.

C. Synthesis Procedures

5 ml of squalane and 5 ml of methyl myristate are transferred into thepot which has been preheated at 100° C. and evacuated for 30 min. (Thesetup includes a 4-neck, 50 mL round bottom flask equipped with a stirbar, a temperature probe and a condenser connected to a N₂/vacuum source(Schlenk line). The flask is heated with a heating mantle connected to adigital temperature controller. The solvent is degassed at 75° C. forone hour and is then placed under N₂ atmosphere.

The InP solution in n-hexane is prepared in a glove box and syringedinto the pot containing the degassed solvent. n-Hexane is removed byvacuum at 75° C. for one hour and then the pot is placed back under N₂atmosphere. The Zn, Se and S precursor solutions are prepared in a glovebox. The calculated amount of 1M TOP-Se and bis-(trimethylsilyl)sulfideis measured out in one vial and loaded into a 5 ml syringe, dilutingwith squalane up to the total volume of 2.0 ml forming theselenide/sulfide precursor solution. The corresponding amount ofdiethylzinc is measured in a vial and loaded into another 5 ml syringewith squalane forming a total of 2.0 ml of zinc precursor solution. Whenthe pot is under N₂ atmosphere at 75° C. after all of the n-hexane hasbeen removed, the two precursor syringes are taken out from the glovebox and connected to capillary tubes and then loaded into a syringepump. The two ends of the capillaries are plunged into the flask. Thetemperature is set to 200° C., and once it reaches 170° C. the precursorsolutions are injected at the rate of 2 ml/hr. A few minutes later whenthe temperature is at 200° C., 2 ml of oleylamine is injected into theflask. When the addition is complete, the overcoated nanocrystals arepreferably annealed prior to crash-out (e.g., precipitation from thereaction mixture) e.g., the temperature is set to 150° C. and leftovernight under N₂ atmosphere. The next day the solution is thensyringed into an evacuated, septum-capped vial for transport into aglove box.

D. Crashing-Out Procedures

Upon cooling, a flocculent, reddish solid precipitates out of the redreaction mixture. The reaction mixture is reheated to 70° C. tore-dissolve the solid, forming a red, homogenous solution. The mixtureis diluted with 20 ml of n-hexane and cooled down long enough for thesolid to precipitate. After being centrifuged (4000 rpm for 8 min), thered supernatant is decanted and collected and the reddish solids arewashed with 10 ml of n-hexane and centrifuged again. The supernatant isdecanted off and added to the first fraction. 20 ml of n-butanol isadded to the red nanocrystal solution followed by enough methanol tomake the solution turbid (typically ˜20 ml). The turbid solution is thencentrifuged and the supernatant is decanted and discarded. The reddishsolid left behind is dissolved in 5 ml n-hexane and filtered through a0.2 μm PTFE syringe filter. Optical properties are obtained in diluten-hexane solution. Photophysical spectra give the first absorption peakof 540-545 nm and emission peak of 570-575 nm with a FWHM=50-55 nm and aquantum yield of 55-60%.

Example 11 InP Nanocrystal Preparation

A. Preparation of the Ligand Solution:

In the glove box, 514 mg (3.21 equivalents) of myristic acid and 215 mg(1.29 equivalents) of amine are weighed out in a septum capped vial.

9 mL of squalane was added to the septum capped vial. The vial wasclosed well, brought out of the glove box and heated to 70° C. in an oilbath under nitrogen atmosphere to dissolve the ligands in squalane.

When the solution became clear after complete dissolution of the ligandsin squalane, the solution is syringed out of the vial and injected intoa preheated, evacuated 4-neck, 50 mL round bottom flask. (Standardindium phosphide setup was used; 4-neck, 50 mL RB was equipped with astir bar, thermocouple temperature probe, condenser w/ N₂/vacuuminlet/outlet, and septa on the remaining necks. All connections werestandard 14/20 ground glass joints lubricated with siliconegrease—except septa, which were secured with copper wire. Flask wasevacuated at 100° C. heated with a heating mantle connected to a digitaltemperature controller.)

The contents were further degassed again at 100° C. for approximately 60minutes. The contents of the ligand solution along with the equivalentsand moles used are given in the table below.

FW moles Equiv- Quan- Compound CAS # (g/mol) (mmol) alents tity UnitsMyristic acid 544-63-8 228.37 3.4086 3.21 550 mg Dioctylamine 1120-48-5241.46 0.9679 1.29 234 mg Squalane 111-01-3 422.81 Solvent 13 mLB. Preparation of Solutions of the Precursors for Injection:In the Glove Box,

120 mg (1 equivalent) of trimethyl indium was dissolved in 1 mL of octylether in a septum capped vial. The solution is then transferred from thevial into a 3 mL syringe fitted with a gauge 12 needle. The syringe tipis then capped by the empty septum capped vial to avoid any aircontamination (when the syringes are brought out of the glove box).

94 mg (0.5 equivalents) of tris-(trimethylsilyl)-phosphine was dissolvedin 1 mL of squalane in another septum capped vial. This solution isagain transferred into a separate 3 mL syringe fitted with a gauge 12needle. The syringe tip is again capped by the empty septum capped vialsimilar to that of the syringe containing trimethyl indium. The reagentsand the solvents used for injection are given in the table below.

Syringe 1:

Com- FW Moles Equiv- Quan- pound CAS# (g/mol) (mmol) alents tity UnitsInMe₃ 15573-38- 250.54 0.750328269 1 120 mg 3 Octyl 629-82-3 242.44Solvent 1 mL etherSyringe 2:

Compound CAS # FW (g/mol) Moles (mmol) Equivalents Quantity UnitsP(TMS)₃ 15573-38-3 250.54 0.37518959 0.500033927 94 mg Squalane 111-01-3422.81 Solvent 1 mL

The reaction flask containing the ligand solution is backfilled withnitrogen and maintained under nitrogen atmosphere. Any deposition ofligand material at the top of the flask was melted down into the flasksolution by gently heating the top outer surface of the flask and thecondenser with a heat gun. The temperature of the flask was then raisedto 175° C.

The vial capped syringes containing the precursor solutions (trimethylindium and tristrimethylsilyl phosphine) were brought out of the glovebox and kept inserted in the septa of the flask (ready for injection).

When the temperature reached above 175° C., the temperature of thetemperature controller is reduced to 168° C. When the temperature of theflask dropped just to 175° C., the precursor solutions are injectedrapidly from the syringes into the contents of the flask and a stopclock was simultaneously started to monitor the time of the reaction.Due to injection, the temperature generally dropped to 168° C. Duringthe reaction, the temperature of the flask was generally maintainedbetween 165° C. and 171° C.

During the reaction, samples of the reaction mixture are extractedthrough 1 mL syringes fitted with longer needles and analyzed forabsorption and emission wavelengths and the corresponding full widthhalf maximum of the emission wavelength peak using the respective Varianspectrophotometer.

When the emission wavelength reached 617 nm with a full width halfmaximum value of 57 nm, the reaction mixture was cooled rapidly using anice bath to room temperature.

The cooled reaction mixture was then transferred into an evacuatedseptum capped vial using a 20 mL syringe and the septum capped vial wastaken into the glove box to isolate the nanoparticles from the reactionmixture.

C. Preparation of the Ligand Solution:

Myristic Dioctyl Degassing Degas temperature Acid amine (mg) Squalane(ml) time (min) (° C.) 550 234 13 60 100D. Injection Reagents and Injection Conditions:

Post- Syringe 1 Syringe 2 Injection injection InMe₃ Octyl P(TMS)₃Squalane Temperature Temperature (mg) ether (ml) (mg) (ml) (° C.) (° C.)120 3 94 3 175 168E. Other Details:

Growth Reaction Temperature (° C.) Time (min) Sampling Quenching 165-17120 2, 4, 6, 8, 10, 15, Ice bath cooling 20F. Experimental Results:

Time (min) Absorption (λ) Emission (λ) FWHM (λ) 2 535 588 61 4 543 59354 6 553 598 52 8 559 606 53 10 567 607 54 15 572 613 58 20 579 617 57

Example 12 InP Nanocrystal Preparation

A. Preparation of the Ligand Solution:

In the glove box, 272 mg (1.5 equivalents) of amine is weighed out in a20 mL vial. 9 mL of squalane was added to the 20 mL vial. The contentsof the vial were mixed well and transferred into a 10 mL syringe. Theneedle of the syringe was capped with the needle cap.

The syringe was brought out of the glove box and its contents wereinjected into a preheated, evacuated 4-neck, 50 mL round bottom flask.(Standard indium phosphide setup was used; 4-neck, 50 mL RB was equippedwith a stir bar, thermocouple temperature probe, condenser w/ N₂/vacuuminlet/outlet, and septa on the remaining necks. All connections werestandard 14/20 ground glass joints lubricated with siliconegrease—except septa, which were secured with copper wire. Flask wasevacuated at 100° C. heated with a heating mantle connected to a digitaltemperature controller.)

The contents were further degassed again at 100° C. for approximately 60minutes. The contents of the ligand solution along with the equivalentsand moles used are given in the table below.

FW moles Equiv- Quan- Compound CAS # (g/mol) (mmol) alents tity UnitsDioctylamine 1120-48-5 241.46 1.1255 1.29 272 mg Squalane 111-01-3422.81 Solvent 11 mLB. Preparation of Solutions of the Precursors for Injection:In the Glove Box,

531 mg (3.1 equivalents) of myristic acid was weighed out in a septumcapped vial. 2 mL of squalane was added to the vial. The vial was cappedtightly.

120 mg (1 equivalent) of trimethyl indium was dissolved in 1 mL of octylether in a septum capped vial. The solution is then transferred from thevial into a 3 mL syringe fitted with a gauge 12 needle. The syringe tipwas then capped by the empty septum capped vial to avoid any aircontamination (when the syringes are brought out of the glove box).

94 mg (0.5 equivalents) of tris-(trimethylsilyl)-phosphine was dissolvedin 1 mL of squalane in another septum capped vial. This solution isagain transferred into a separate 3 mL syringe fitted with a gauge 12needle. The syringe tip is again capped by the empty septum capped vialsimilar to that of the syringe containing trimethyl indium. The reagentsand the solvents used for injection are given in the table below.

Syringe 1:

Com- FW Moles Equiv- Quan- pound CAS# (g/mol) (mmol) alents tity UnitsInMe₃ 15573-38-3 250.54 0.750328269 1 120 mg Octyl 629-82-3 242.44Solvent 1 mL etherSyringe 2:

Moles Compound CAS # FW (g/mol) (mmol) Equivalents Quantity UnitsP(TMS)₃ 15573-38-3 250.54 0.37518959 0.500033927 94 mg Squalane 111-01-3422.81 Solvent 1 mL

The reaction flask containing the ligand solution is backfilled withnitrogen and maintained under nitrogen atmosphere. The temperature ofthe flask was then raised to 185 C.

The two syringes and the vial containing the myristic acid were broughtout of the glove box. The vial capped syringes containing the precursorsolutions (trimethyl indium and tris-(trimethylsilyl)-phosphine) werekept inserted in the septa of the flask (ready for injection).

In the meantime, the septum capped vial containing myristic acid washeated in an oil bath under nitrogen atmosphere at 70° C. to dissolveall the myristic acid.

When the temperature of the flask stabilized at 185° C., the precursorsolutions were injected rapidly from the syringes into the contents ofthe flask. The temperature dropped to around 170° C. While thetemperature was allowed to rise back to 185° C., the heated myristicacid solution was transferred into a 5 mL syringe, fitted with a gauge12 needle and kept inserted in the septum of the flask ready forinjection. It took approximately 3 to 4 minutes for the temperature torise back to 185° C.

Syringe 3:

FW Moles Equiv- Quan- Compound CAS # (g/mol) (mmol) alents tity UnitsMyristic 544-63-8 228.37 2.33 3.10 531 mg acid Squalane 111-01-3 422.812 mL

When the temperature rose back to 185° C., the myristic acid solutionwas rapidly injected into the contents of the flask and a stop clock wassimultaneously started to monitor the time of the reaction. Thetemperature dropped to 174° C. The temperature in the digitaltemperature controller was set to 175° C. and maintained between 172° C.and 180° C. during the reaction.

During the reaction, samples of the reaction mixture were extractedthrough 1 mL syringes fitted with longer needles and analyzed forabsorption and emission wavelengths and the corresponding full widthhalf maximum of the emission wavelength peak using the respective Varianspectrophotometer.

When the emission wavelength reached 605 nm with a full width halfmaximum value of 56 nm, the reaction mixture was cooled rapidly using anice bath to room temperature.

The cooled reaction mixture was then transferred into an evacuatedseptum capped vial using a 20 mL syringe and the septum capped vial wastaken into the glove box to isolate the nanoparticles from the reactionmixture.

C. Preparation of the Ligand Solution:

Dioctyl Degassing Degas temperature amine (mg) Squalane (ml) time (min)(° C.) 234 11 60 100D. Injection Reagents and Injection Conditions:

Post- Syringe 1 Syringe 2 Injection injection InMe₃ Octyl P(TMS)₃Squalane Temperature Temperature (mg) ether (ml) (mg) (ml) (° C.) (° C.)120 1 94 1 185 170 Post- Syringe 3 Injection injection Myristic SqualaneTemperature Temperature acid (mg) (ml) (° C.) (° C.) 531 2 185 174E. Other Details:

Growth Reaction Temperature (° C.) Time (min) Sampling Quenching 172-18020 5, 8, 13, 18, 23, Ice bath cooling 30, 37F. Experimental Results:

Time (min) Absorption (λ) Emission (λ) FWHM (λ) 5 500 552 57 8 516 55851 13 519 563 49 18 527 573 51 23 538 576 55 30 548 582 58 37 555 605 56

The foregoing description and example have been set forth merely toillustrate the invention and are not intended as being limiting. Each ofthe disclosed aspects and embodiments of the present invention may beconsidered individually or in combination with other aspects,embodiments, and variations of the invention.

In addition, unless otherwise specified, none of the steps of themethods of the present invention are confined to any particular order ofperformance.

Nanocrystals comprising semiconductor material show strong quantumconfinement effects that can be harnessed in designing bottom-upchemical approaches to create complex heterostructures with electronicand optical properties that are tunable with the size and composition ofthe nanocrystals.

When an electron and hole localize on a semiconductor nanocrystal,emission can occur at an emission wavelength. The emission has afrequency that corresponds to the band gap of the quantum confinedsemiconductor material. The band gap is a function of the size of thesemiconductor nanocrystal. Semiconductor nanocrystals having smalldiameters can have properties intermediate between molecular and bulkforms of matter. For example, semiconductor nanocrystals based onsemiconductor materials having small diameters can exhibit quantumconfinement of both the electron and hole in all three dimensions, whichleads to an increase in the effective band gap of the material withdecreasing crystallite size. Consequently, both the optical absorptionand emission of semiconductor nanocrystals shift to the blue, or tohigher energies, as the size of the crystallites decreases.

The emission from a semiconductor nanocrystal can be a narrow Gaussianemission band that can be tuned through the complete wavelength range ofthe ultraviolet, visible, or infra-red regions of the spectrum byvarying the size of the semiconductor nanocrystal, the composition ofthe semiconductor nanocrystal, or both. For example, CdSe can be tunedin the visible region and InAs can be tuned in the infra-red region. Thenarrow size distribution of a population of semiconductor nanocrystalscan result in emission of light in a narrow spectral range. As discussedabove, the population can be monodisperse preferably exhibits less thana 15% rms (root-mean-square) deviation in diameter of the semiconductornanocrystals, more preferably less than 10%, most preferably less than5%. Spectral emissions in a narrow range of no greater than about 75 nm,preferably 60 nm, more preferably 40 nm, and most preferably 30 nm fullwidth at half max (FWHM) for semiconductor nanocrystals that emit in thevisible can be observed. IR-emitting semiconductor nanocrystals can havea FWHM of no greater than 150 nm, or no greater than 100 nm. The breadthof the emission decreases as the dispersity of semiconductor nanocrystaldiameters decreases. Semiconductor nanocrystals in accordance with theinvention can have photoluminescence quantum efficiencies greater thanabout 30%, greater than about 40%, greater than about 50%.

The narrow FWHM of semiconductor nanocrystals can result in saturatedcolor emission. This can lead to efficient lighting devices, forexample, in the red parts of the visible spectrum, since insemiconductor nanocrystal emitting devices no photons are lost toinfra-red and UV emission. The broadly tunable, saturated color emissionover the entire visible spectrum of a single material system isunmatched by any class of organic chromophores (see, for example,Dabbousi et al., J. Phys. Chem. 101, 9463 (1997), which is incorporatedby reference in its entirety). A monodisperse population ofsemiconductor nanocrystals will emit light spanning a narrow range ofwavelengths. A device including semiconductor nanocrystals of differentcompositions, sizes, and/or structures can emit light in more than onenarrow range of wavelengths. The color of emitted light perceived by aviewer can be controlled by selecting appropriate combinations ofsemiconductor nanocrystal sizes and materials in the device as well asrelative subpixel currents. The degeneracy of the band edge energylevels of semiconductor nanocrystals facilitates capture and radiativerecombination of all possible excitons, whether generated by directcharge injection or energy transfer. The maximum theoreticalsemiconductor nanocrystal lighting device efficiencies are thereforecomparable to the unity efficiency of phosphorescent organiclight-emitting devices. The excited state lifetime (τ) of thesemiconductor nanocrystal is much shorter (τ˜10 ns) than a typicalphosphor (τ>0.1 μs), enabling semiconductor nanocrystal lighting devicesto operate efficiently even at high current density and high brightness.

Nanocrystals can be suitable for a variety of applications, includingthose disclosed in U.S. patent application Ser. No. 09/156,863, filedSep. 18, 1998 (now U.S. Pat. No. 6,251,303), Ser. No. 09/160,454, filedSep. 24, 1998 (now U.S. Pat. No. 6,326,144), Ser. No. 09/160,458, filedSep. 24, 1998 (now U.S. Pat. No. 6,617,583), Ser. No. 09/350,956, filedJul. 9, 1999 (now U.S. Pat. No. 6,803,719), and Ser. No. 10/400,908,filed Mar. 28, 2003 (U.S. Published Patent Application No. 20040023010),all of which are incorporated herein by reference in their entirety.

For example, nanocrystals comprising semiconductor material can be usedin optoelectronic devices including electroluminescent devices such aslight emitting diodes (LEDs) or alternating current thin filmelectroluminescent devices (ACTFELDs).

Light-emitting devices can be used to provide illumination. Lightemitting devices also can be included, for example, in displays (e.g.,flat-panel displays), screens (e.g., computer screens), and other itemsthat require illumination. Accordingly, increases in the efficiency of alight-emitting device can improve the viability of producing emissivedevices.

Light-emitting devices including nanocrystals comprising semiconductormaterial can be made, for example, by spin-casting a solution containingthe hole transport layer (HTL) organic semiconductor molecules and thenanocrystals, where the HTL forms underneath the nanocrystal layer viaphase separation (see, for example, U.S. patent application Ser. Nos.10/400,907 and 10/400,908, both filed Mar. 28, 2003, each of which isincorporated by reference in its entirety). In certain embodiments, thisphase separation technique can be used to place a monolayer ofnanocrystals between an organic semiconductor HTL and electron transportlayer (ETL), thereby effectively exploiting the favorable light emissionproperties of nanocrystals, while minimizing their impact on electricalperformance. Other techniques for depositing nanocrystals includeLangmuir-Blodgett techniques and drop-casting. Some techniques fordepositing nanocrystals may not be well suited for all possiblesubstrate materials, may involve use of chemicals that can affect theelectrical or optical properties of the layer, may subject the substrateto harsh conditions, and/or may place constraints on the types ofdevices that can be grown in some way. Other techniques discussed belowmay be preferable if a patterned layer of nanocrystals is desired.

Preferably, nanocrystals comprising semiconductor material are processedin a controlled (oxygen-free and moisture-free) environment, preventingthe quenching of luminescent efficiency during the fabrication process.

In certain embodiments, nanocrystals comprising semiconductor material(also referred to as semiconductor nanocrystals) can be deposited in apatterned arrangement. Patterned semiconductor nanocrystals can be usedto form an array of pixels comprising, e.g., red, green, and blue oralternatively, red, yellow, green, blue-green, and/or blue emitting, orother combinations of distinguishable color emitting subpixels, that areenergized to produce light of a predetermined wavelength.

An example of a technique for depositing a light-emitting materialcomprising semiconductor nanocrystals in a pattern and/or in amulti-color pattern or other array is contact printing. Contact printingadvantageously allows micron-scale (e.g., less than 1 mm, less than 500microns, less than 200 microns, less than 100 microns, less than 50microns, less than 25 microns, or less than 10 microns) patterning offeatures on a surface. Pattern features can also be applied at largerscales, such as 1 mm or greater, 1 cm or greater, 1 m or greater, 10 mor greater. Contact printing can allow dry (e.g., liquid free orsubstantially liquid free) application of a patterned semiconductornanocrystal layer to a surface. In a pixilated device, the semiconductornanocrystal layer comprises a patterned array of the semiconductornanocrystals on the underlying layer. In instances where a pixelincludes subpixels, the sizes of the subpixels can be a proportionatefraction of the pixel size, based on the number of subpixels.

Additional information and methods for depositing semiconductornanocrystals are described in U.S. patent application Ser. No.11/253,612 entitled “Method And System For Transferring A PatternedMaterial”, filed 21 Oct. 2005, and Ser. No. 11/253,595 entitled “LightEmitting Device Including Semiconductor Nanocrystals”, filed 21 Oct.2005, each of which is hereby incorporated herein by reference in itsentirety.

A non-limiting example of an embodiment of a device includingsemiconductor nanocrystals in accordance with the invention can beprepared as follows.

Glass (50 mm×50 mm) with patterned indium tin oxide (ITO) electrode onone surface (e.g., obtained from Thin Film Devices, Anaheim, Calif.) ispreferably cleaned in an oxygen plasma for a suitable time (e.g., about6 minutes) to remove contaminants and oxygenate the surface. Forexample, the cleaning is carried out in 100% oxygen at about 20 psi. Theglass can be placed on a water cooled plate to help control the increasein temperature during cleaning.

A layer of hole injection material (e.g., PEDOT, obtained from H.C.Starck, GmbH) (HIL) is spun onto the surface of the glass including thepatterned electrode at a predetermined speed (e.g., 4000 RPM) to adesired thickness (e.g., about 750 Angstroms). This step can be carriedout under ambient conditions (i.e., not in a glove box). Preferably, thePEDOT coated glass is then heated on a 120° C. hot plate in a chamber(<20 ppm water & <10 ppm oxygen), in a HEPA filter environment (approx.Class 1), in a nitrogen atmosphere for >20 minutes to dry the PEDOT. ThePEDOT coated glass is then allowed to cool to room temperature.

A layer of hole transport material (e.g.,N,N′-bis(3-methylphenyl)-N,N′-bis(phenyl)-spiro (spiro-TPD) (E105—OLEDgrade, gradient sublimation purified) from Luminescent Technologies,Taiwan)) is then evaporated onto the PEDOT layer in a deposition chamber(an Å MOD chamber, obtained from Angstrom Engineering, Ottowa, Canada)to a desired thickness (e.g., about 500 Angstroms) after pumping thechamber down to 10⁻⁶ torr or better.

The spiro-TPD coated glass is then returned to the nitrogen environmentand stamped with an ink including nanocrystals in accordance with theinvention and hexane. A typical optical density of the dispersion of thesemiconductor nanocrystals in the ink can be, e.g., 0.02, although otheroptical densities can be selected by the skilled artisan. The ink isstamped onto the spiro-TPD layer using an unfeatured curved Parylene-Ccoated PDMS stamp using a pad printing machine, e.g., printing machinemodel XP-05 made by Pad Printing Machinery of Vermont.

After printing, the device is returned to the deposition chamber and ispumped back down to 10-⁶ torr or better for evaporation of the nextlayer, which can be a hole blocking layer or an electron transportlayer.

A layer of electron transport material (e.g., LT-N820 from LuminescentTechnologies, Taiwan) is deposited to a desired thickness (e.g., about500 Angstroms).

Each of the vapor deposited layers can be patterned with use of shadowmasks. After deposition of the electron transport material layer, themask is changed before deposition of the metal cathode (e.g., LiF (5Angstrom)/Al (1000 Angstrom)).

Alternative hole and electron transport materials, electrode materials,and layer thicknesses can be used. Optionally, additional layers andstructures, as discussed herein, can also be included in a device.

A device in accordance with the invention can further include abackplane. A backplane can include active or passive electronics forcontrolling or switching power to individual light-emitting devices orpixels. In particular, the backplane can be configured as an activematrix, passive matrix, fixed format, direct drive, or hybrid. Thedevice including multiple light-emitting devices or pixels can beconfigured for still images, moving images, or lighting.

Other materials, techniques, methods and applications that may be usefulwith the present invention are described in, U.S. Provisional PatentApplication No. 60/792,170, of Seth Coe-Sullivan, et al., for“Composition Including Material, Methods Of Depositing Material,Articles Including Same And Systems For Depositing Material”, filed on14 Apr. 2006; U.S. Provisional Patent Application No. 60/792,084, ofMaria J. Anc, For “Methods Of Depositing Material, Methods Of Making ADevice, And System”, filed on 14 Apr. 2006, U.S. Provisional PatentApplication No. 60/792,086, of Marshall Cox, et al, for “Methods OfDepositing Nanomaterial & Methods Of Making A Device” filed on 14 Apr.2006; U.S. Provisional Patent Application No. 60/792,167 of SethCoe-Sullivan, et al, for “Articles For Depositing Materials, TransferSurfaces, And Methods” filed on 14 Apr. 2006, U.S. Provisional PatentApplication No. 60/792,083 of LeeAnn Kim et al., for “Applicator ForDepositing Materials And Methods” filed on 14 Apr. 2006; U.S.Provisional Patent Application 60/793,990 of LeeAnn Kim et al., for“Applicator For Depositing Materials And Methods” filed on 21 Apr. 2006;U.S. Provisional Patent Application No. 60/790,393 of Seth Coe-Sullivanet al., for “Methods And Articles Including Nanomaterial”, filed on 7Apr. 2006; U.S. Provisional Patent Application No. 60/805,735 of SethCoe-Sullivan, for “Methods For Depositing Nanomaterial, Methods ForFabricating A Device, And Methods For Fabricating An Array Of Devices”,filed on 24 Jun. 2006; U.S. Provisional Patent Application No.60/805,736 of Seth Coe-Sullivan et al., for “Methods For DepositingNanomaterial, Methods For Fabricating A Device, Methods For FabricatingAn Array Of Devices And Compositions”, filed on 24 Jun. 2006; U.S.Provisional Patent Application No. 60/805,738 of Seth Coe-Sullivan etal., for “Methods And Articles Including Nanomaterial”, filed on 24 Jun.2006; U.S. Provisional Patent Application No. 60/795,420 of Paul Beattyet al., for “Device Including Semiconductor Nanocrystals And A LayerIncluding A Doped Organic Material And Methods”, filed on 27 Apr. 2006;U.S. Provisional Patent Application No. 60/804,921 of Seth Coe-Sullivanet al., for “Light-Emitting Devices And Displays With ImprovedPerformance”, filed on 15 Jun. 2006, U.S. Published Patent ApplicationNo. 20060157720 of Moungi G. Bawendi et al. for “Nanocrystals IncludingIII-V Semiconductors”; U.S. Published Patent Application No. 2006013074of Peng, et al., for “High Quality Colloidal Nanocrystals And Methods OfPreparing The Same In Non-Coordinating Solvents”, PCT Publication No.WO/2005/002007 of Lucey, et al. for “Process For Producing SemiconductorNanocrystal Cores, Core-Shell, Core-Buffer-Shell, And Multiple LayerSystems In A Non-Coordinating Solvent Utilizing In Situ SurfactantGeneration”, U.S. Pat. No. 5,505,928 of A. Paul Alivisatos, et al. for“Preparation of III-V Semiconductor Nanocrystals”, U.S. Provision PatentApplication No. 60/825,373, filed 12 Sep. 2006, of Seth A. Coe-Sullivanet al., for “Light-Emitting Devices And Displays With ImprovedPerformance”; and U.S. Provision Patent Application No. 60/825,374,filed 12 Sep. 2006, of Seth A. Coe-Sullivan et al., for “Light-EmittingDevices And Displays With Improved Performance”. The disclosures of eachof the foregoing listed patent documents are hereby incorporated hereinby reference in their entireties.

Other multilayer structures may optionally be used to improve theperformance of the light-emitting devices and displays of the invention.

The performance of light emitting devices can be improved by increasingtheir efficiency, narrowing or broadening their emission spectra, orpolarizing their emission. See, for example, Bulovic et al.,Semiconductors and Semimetals 64, 255 (2000), Adachi et al., Appl. Phys.Lett. 78, 1622 (2001), Yamasaki et al., Appl. Phys. Lett. 76, 1243(2000), Dirr et al., Jpn. J. Appl. Phys. 37, 1457 (1998), and D'Andradeet al., MRS Fall Meeting, BB6.2 (2001), each of which is incorporatedherein by reference in its entirety. Semiconductor nanocrystals can beincluded in efficient hybrid organic/inorganic light emitting devices.

Because of the diversity of semiconductor nanocrystal materials that canbe prepared, and the wavelength tuning via semiconductor nanocrystalcomposition, structure, and size, devices that are capable of emittinglight of a predetermined color are possible with use of semiconductornanocrystals as the emissive material. Semiconductor nanocrystallight-emitted devices can be tuned to emit anywhere in the spectrum.

Light-emitting devices can be prepared that emit visible or invisible(e.g., IR) light. The size and material of a semiconductor nanocrystalcan be selected such that the semiconductor nanocrystal emits lighthaving a predetermined wavelength. Light emission can be of apredetermined wavelength in any region of the spectrum, e.g., visible,infrared, etc. For example, the wavelength can be between 300 and 2,500nm or greater, for instance between 300 and 400 nm, between 400 and 700nm, between 700 and 1100 nm, between 1100 and 2500 nm, or greater than2500 nm.

Individual light-emitting devices can be formed. In other embodiments, aplurality of individual light-emitting devices can be formed at multiplelocations on a single substrate to form a display. The display caninclude devices that emit at the same or different wavelengths. Bypatterning the substrate with arrays of different color-emittingsemiconductor nanocrystals, a display including pixels of differentcolors can be formed.

An individual light-emitting device or one or more light-emittingdevices of a display can optionally include a mixture of differentcolor-emitting semiconductor nanocrystals formulated to produce a whitelight. White light can alternatively be produced from a device includingred, green, blue, and, optionally, additional pixels.

Examples of other displays are included in U.S. Patent Application No.60/771,643 for “Displays Including Semiconductor Nanocrystals AndMethods Of Making Same”, of Seth Coe-Sullivan et al., filed 9 Feb. 2006,the disclosure of which is hereby incorporated herein by reference inits entirety.

For additional information relating to semiconductor nanocrystals andtheir use, see also U.S. Patent Application No. 60/620,967, filed Oct.22, 2004, and Ser. No. 11/032,163, filed Jan. 11, 2005, U.S. patentapplication Ser. No. 11/071,244, filed 4 Mar. 2005. Each of theforegoing patent applications is hereby incorporated herein by referencein its entirety.

As used herein, the singular forms “a”, “an” and “the” include pluralunless the context clearly dictates otherwise. Thus, for example,reference to an emissive material includes reference to one or more ofsuch materials.

Applicants specifically incorporate the entire contents of all citedreferences in this disclosure. Further, when an amount, concentration,or other value or parameter is given as either a range, preferred range,or a list of upper preferable values and lower preferable values, thisis to be understood as specifically disclosing all ranges formed fromany pair of any upper range limit or preferred value and any lower rangelimit or preferred value, regardless of whether ranges are separatelydisclosed. Where a range of numerical values is recited herein, unlessotherwise stated, the range is intended to include the endpointsthereof, and all integers and fractions within the range. It is notintended that the scope of the invention be limited to the specificvalues recited when defining a range.

Other embodiments of the present invention will be apparent to thoseskilled in the art from consideration of the specification and practiceof the invention disclosed herein. It is intended that the specificationand examples be considered as exemplary only, with a true scope andspirit of the invention being indicated by the following claims andequivalents thereof.

What is claimed is:
 1. A composition comprising a matrix and ananocrystal comprising a core comprising a first semiconductor materialcomprising one or more elements of Group IIIA of the Periodic Table ofElements and one or more elements of Group VA of the Periodic Table ofElements, and a shell disposed over at least a portion of a surface ofthe core, the shell comprising one or more additional semiconductormaterials, wherein the nanocrystal is capable of emitting visible lighthaving a photoluminescence quantum efficiency of at least about 30% uponexcitation.
 2. A composition in accordance with claim nanocrystal inaccordance with claim 1 wherein the nanocrystal is capable of emittinglight including a maximum peak emission at a wavelength in the rangefrom about 500 nm to about 700 nm upon excitation.
 3. A composition inaccordance with claim nanocrystal in accordance with claim 1 wherein thenanocrystal is capable of emitting light including a maximum peakemission at a wavelength in the range from about 560 nm to about 650 nmupon excitation.
 4. A composition in accordance with claim 1 wherein theemitted light has a maximum peak emission with a FWHM less than 70 nm.5. A composition in accordance with claim 1 wherein the emitted lighthas a maximum peak emission with a FWHM less than 60 nm.
 6. Acomposition in accordance with claim 1 wherein the matrix comprises apolymer.
 7. A composition in accordance with claim 1 wherein the matrixcomprises a glass.
 8. A composition in accordance with claim 1 whereinthe matrix comprises a photo-polymerizable resin.
 9. A composition inaccordance with claim 1 wherein the matrix further includes scatterers.